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ESP game

The ESP Game is a two-player online computer game developed by Luis von Ahn and Laura Dabbish at Carnegie Mellon University, first launched in 2003, that crowdsources descriptive labels for web images by turning the task into an engaging matching challenge.^[1] Players are randomly paired and shown the same unlabeled image, tasked with typing words they believe describe it without communicating; when both enter the same word, they score points and the label is added to the image's metadata, while previously agreed-upon "taboo" words are hidden to encourage diverse descriptors.^[1] Each game session lasts approximately 2.5 minutes, with images selected from sources like Google to prioritize those needing labels for applications such as improved image search, accessibility for visually impaired users, and content filtering.^[1] As the inaugural example of "Games with a Purpose" (GWAP), a framework introduced by von Ahn to solve computational problems through fun, human-powered activities, the ESP Game demonstrated the viability of gamification for large-scale data annotation.^[2] In its initial four months online, it attracted 13,630 players who generated 1,271,451 labels across 293,760 images, achieving near-100% precision in tested labels and projecting that 5,000 active players could label Google's entire 425 million-image corpus in just 31 days.^[1] The game's design addressed key challenges in image labeling, such as subjectivity and tedium, by leveraging players' natural agreement on common descriptors while mitigating cheating through real-time pairing and scoring mechanics.^[1] The ESP Game's influence extended beyond academia when Carnegie Mellon licensed it to Google in 2006, leading to the launch of Google Image Labeler—a rebranded version integrated into Google Labs that similarly paired users to tag images for enhancing search relevance.^[2] Google discontinued Image Labeler in September 2011 as part of a broader service cleanup to focus resources on high-impact offerings.^[3] In 2016, Google relaunched image labeling efforts through Google Crowdsource, a non-gamified crowdsourcing platform that includes verification tasks for improving AI datasets like Open Images and remains active as of 2025.^[4] Despite its operational end, the ESP Game pioneered human computation techniques that continue to inspire crowdsourcing platforms and AI training datasets, underscoring the power of playful incentives in bridging human perception with machine learning.^[2]

Overview

Concept

The ESP Game is an online multiplayer game launched on August 9, 2003, that pairs anonymous players randomly to describe the same image using descriptive words, requiring them to agree on labels without any direct communication between partners.^[1] Developed as a form of human computation, it transforms the labor-intensive task of image annotation into an engaging activity by leveraging players' natural perceptual abilities and desire for entertainment.^[1] At its core, the game's purpose is to generate alternative text labels for web images, thereby improving search engine accessibility, enabling more effective reverse image search, and supporting content-based filtering for applications like parental controls.^[1] This addresses the longstanding "image labeling problem" in artificial intelligence, where computers have historically struggled to interpret visual content due to limitations in computer vision technology at the time.^[1] By crowdsourcing labels from human players, the ESP Game creates high-quality datasets that can train machine learning models to better understand and categorize images.^[1] The game's interface, implemented as a Java applet, presents players with a shared image, where they type words in real-time to anticipate and match their partner's guesses, fostering rapid consensus on relevant descriptors.^[1] This setup exploits the commonality in human descriptions of visuals, allowing the system to collect diverse yet agreed-upon labels efficiently through playful interaction.^[1]

History and Development

The ESP Game was created in 2003 by Luis von Ahn, then a PhD student in computer science at Carnegie Mellon University, in collaboration with Laura Dabbish, as part of his research on human computation paradigms that harness collective human effort to address computational challenges beyond the capabilities of machines alone.^[1] This work laid foundational groundwork for the broader concept of Games With A Purpose (GWAP), where entertainment drives useful data generation, later formalized in von Ahn's 2006 publication.^[5] Development of the game was supported by grants from the National Science Foundation, specifically CCR-0122581 and CCR-0085982 through the Aladdin Center, along with a Microsoft Research Fellowship for von Ahn and a National Defense Science and Engineering Graduate Fellowship for Dabbish.^[1] The game's design was first detailed in the 2004 CHI conference paper "Labeling Images with a Computer Game" by von Ahn and Dabbish, which described its mechanics for image annotation and presented preliminary empirical results demonstrating its efficacy in producing high-quality labels through paired player agreement.^[1] The ESP Game launched publicly on August 9, 2003, via the website espgame.org, implemented as a Java applet to facilitate real-time online play.^[1] It achieved rapid adoption, with 13,630 unique players generating 1,271,451 labels for 293,760 images between launch and December 10, 2003, and over 80% of participants returning for multiple sessions.^[1] By September 2006, the game had engaged more than 75,000 unique players, underscoring its appeal and scalability in crowdsourcing image metadata.^[6] A key milestone occurred in 2006 when Google licensed the ESP Game's technology to develop Google Image Labeler, integrating player-generated labels to enhance the accuracy of its image search engine.^[7] The original espgame.org site was shut down in 2011.^[8]

Gameplay Mechanics

Core Rules

The ESP Game pairs players randomly with an anonymous partner online, preventing any direct communication to ensure independent inputs. The interface presents a sequence of images sourced from web crawls, displayed one at a time in a session, with players tasked with describing visible content to generate useful labels as a byproduct of gameplay.^[1] Players input single words or short phrases via text fields, aiming to exactly match their partner's description of the shared image. Successful matches are revealed instantly to both, advancing the labeling for that image; the system displays up to six taboo words—prior agreements on the image—to promote varied and specific labels. The round for an image concludes after multiple matches or mutual passes, with the game progressing through up to 15 images per session. Players can mutually pass on challenging images to skip them efficiently.^[1] Scoring incentivizes participation by awarding points to both players for each exact match, fostering quick consensus on descriptive terms. A substantial bonus is granted upon completing agreements for all 15 images in a session. Session totals are shown upon completion, highlighting cumulative achievements.^[1] Each game session runs for 2.5 minutes, allowing rapid cycling through images to maximize engagements within a short timeframe. Players may end early or skip via passes but are encouraged to continue for higher scores; multiple sessions can be played daily without formal restrictions. There is no defined win condition or endgame, but emphasis on accumulating high scores drives sustained play.^[1]

Player Interaction and Matching

In the ESP Game, players are anonymously paired by a centralized server algorithm that randomly matches online participants at any given time, with new pairings initiated every 30 seconds to facilitate continuous play. To prevent collusion, the system ensures that players are not matched with the same partner more than once and verifies distinct IP addresses to avoid self-pairing or coordinated cheating attempts. These one-session matches, typically consisting of 15 images, promote independent contributions without prior familiarity, fostering a dynamic environment where thousands of players can contribute simultaneously without direct coordination.^[1] Player interaction relies entirely on indirect communication, as participants see only their own typed inputs and any resulting matches, with no chat functionality, shared visuals of partner actions, or other cues available. This design compels players to anticipate common descriptive language for the same image, such as both entering "dog" to label a canine, relying on shared cultural and linguistic conventions to achieve consensus. The absence of direct contact encourages players to "think like each other," building agreement through trial-and-error guesses limited to 13 characters each, which are submitted in real time.^[1] The matching algorithm performs real-time string comparisons on the server side, requiring exact word matches for agreement—partial matches or synonyms are not accepted to ensure data simplicity and quality. Successful matches are confirmed only when both players independently provide identical labels, advancing the shared set of images. Feedback is provided through visual cues, including a thermometer-style progress bar that fills as agreements accumulate toward completing the session's image tab, enhancing player engagement without revealing partner-specific details.^[1] This interaction model cultivates social dynamics centered on creative yet convergent thinking, where players gravitate toward stereotypical or obvious labels to maximize matches, such as tagging ocean scenes with "beach" due to common associations. Studies analyzing game-generated metadata reveal that these dynamics often amplify linguistic biases, leading to predictable descriptors that reflect societal stereotypes, though this convergence boosts agreement rates and overall label volume—1,271,451 labels across 293,760 images from 13,630 players in the initial four months.^[1]^[9]

Technical Implementation

Image Selection Process

The ESP Game draws its image pool primarily from Google's image database, accessed via tools like Random Bounce Me to query random web pages and collect diverse visuals in formats such as JPEG and GIF.^[1] This method ensures a broad selection without manual curation, amassing an initial database of approximately 350,000 images to support ongoing gameplay.^[1] Automated filters are applied during selection to exclude unsuitable content, such as blank images, single-color graphics, those smaller than 20 pixels in any dimension, or visuals with extreme aspect ratios greater than 4.5 or less than 1/4.5.^[1] To avoid sensitive material like pornography, additional text-based filters and theme-based segregation are employed, particularly in versions adapted for broader audiences including children.^[1] The algorithm further prioritizes images based on ambiguity and existing metadata scarcity, favoring those with low prior label agreement—such as abstract art, memes, or controversial visuals—that have been frequently passed over in previous sessions, as these yield the most valuable new data.^[1] Images are presented in a randomized order within each gameplay session to minimize bias and maintain engagement, with each visual rescaled to a uniform display size suitable for the game's applet, typically without accompanying captions or contextual hints.^[1] Diversity is maintained through random web sourcing.^[1] This process dynamically refines the selection to emphasize under-labeled assets while discarding those presumed fully annotated or excessively difficult.^[1]

Labeling and Data Generation

In the ESP Game, labels are collected whenever a pair of players independently enters the same word for an image, generating a weighted label based on the frequency of such agreements across multiple player pairs. This frequency-based scoring reflects the consensus strength of each word, with more agreements indicating higher reliability. Labels achieving at least one agreement (threshold X=1) are considered valid, and previously agreed words become taboo for future pairs on the same image to encourage diversity.^[1] The validation process ranks proposed labels by their agreement rate, promoting high-consensus terms—typically those with repeated matches from independent pairs—as official descriptors suitable for alt-text in web accessibility. For instance, evaluator assessments showed that labels achieving strong agreement were descriptive in 85% of cases, while lower-consensus or ambiguous terms are discarded or the image requeued for additional playthroughs to build further consensus. Quality control incorporates filters to exclude non-descriptive spam words (e.g., "image" or "picture") and blacklists for inappropriate content like profanity, alongside statistical outlier detection via rater reviews to prioritize relevant nouns and adjectives. Random player pairing and taboo word lists further mitigate repetitive or low-value inputs.^[1] The resulting data output comprised over 1.2 million labels for approximately 300,000 images within the first four months of the game's 2003 launch, expanding to more than 10 million labels by 2006 through widespread adoption.^[1]^[5] These datasets were used in research for applications such as improved image search and accessibility, with player metadata anonymized to preserve privacy.^[1] The system's scalability supported peak engagement from 13,000 players, generating thousands of labels daily at launch and demonstrating capacity for 5,000 active players to process Google's 425 million-image corpus in 31 days.^[1]^[10]

Challenges and Limitations

Cheating Detection

In the ESP Game, common cheating tactics included collusion through external communication channels, such as coordinating via phone or chat to share labels in advance, which allowed players to achieve rapid agreements without genuine effort.^[1] Other tactics involved repetitive irrelevant entries, like typing a fixed word such as "a" for every image to farm points quickly, or self-pairing, where a player used multiple accounts from the same device to control both sides of the game.^[1] Detection techniques relied on anomaly monitoring, such as tracking unnatural match speeds where a sharp decrease in average agreement time indicated coordinated cheating.^[1] IP address tracking was employed to prevent multi-accounting by ensuring partners had distinct IPs, flagging sessions from the same location for review.^[1] Additionally, random player queuing and pairing from a large pool minimized the chance of colluders matching, while test images with known labels helped identify suspicious behavior through inconsistent responses.^[11] Response measures included inserting bot players with pre-recorded actions to disrupt global cheating strategies, rendering coordinated inputs ineffective.^[1] Labels from potentially cheated games were weighted lower or excluded by enforcing a "good label" threshold requiring agreement from multiple independent player pairs (e.g., at least two or more).^[1] Temporary session disruptions, such as introducing taboo words that blocked repeated strategies for the duration of a game, further deterred abuse without permanent exclusions.^[1] Statistical safeguards involved dynamically adjusting agreement thresholds to demand consensus from diverse player pairs, reducing the impact of any single collusive group.^[11] These methods, combined with the game's design emphasizing fun over competition, ensured that cheating did not significantly corrupt the dataset, as even partial invalid entries were filtered out through redundancy.^[1]

Ethical and Privacy Concerns

The ESP Game's design involves collecting user data such as IP addresses to detect and prevent cheating through random player pairing and session monitoring, alongside typed labels for image annotation, which could enable behavioral profiling and potential deanonymization of participants despite no explicit intent for such use.^[1] Additionally, the game's image corpus is drawn from public web sources, which may inadvertently include personal photographs of identifiable individuals, raising concerns about the privacy of those depicted without their knowledge or consent for inclusion in a crowdsourced labeling system.^[1] The game also faced challenges in filtering inappropriate content from web images, potentially exposing players to unsuitable material.^[1] Players contribute to the game under limited transparency regarding data repurposing, often unaware that their labels train commercial AI applications, such as enhancements to Google's image search functionality, with no mechanisms provided for opting out of downstream proprietary uses.^[12] This lack of informed consent undermines user autonomy, as the game's entertaining format masks its role in generating high-value training data for machine learning models. The labeling process amplifies biases inherent to the player base, which consists primarily of young, English-speaking users from Western demographics, resulting in datasets that overrepresent cultural norms and underrepresent diverse global traditions.^[1] These skewed annotations propagate into trained AI systems, perpetuating inequities in applications like image recognition. Additionally, labels may require periodic re-labeling as linguistic and cultural associations evolve over time.^[1] Critics have highlighted the game's reliance on unpaid "human computation" as a form of labor exploitation, where participants inadvertently provide economically valuable data for AI development—such as the millions of labels collected for Google's systems—without fair compensation or recognition of their contributions as work.^[12]^[13] To mitigate these issues, the ESP Game incorporates basic anonymization by not storing persistent user identifiers beyond session needs and includes terms of service disclosures about data collection for research and improvement purposes.^[1] Creator Luis von Ahn has since advocated for ethical frameworks in games with a purpose (GWAP), emphasizing transparency, fun as intrinsic motivation, and societal benefit in his broader human computation research to balance utility with participant rights.^[14]

Impact and Legacy

Applications in Computer Vision

The ESP Game's labels were integrated into Google Image Search through its licensing and reimplementation as the Google Image Labeler in 2006, enabling the addition of user-generated keywords to improve search relevance and accuracy.^[15] This collaboration allowed for the annotation of millions of web images, with labels directly enhancing query results by associating descriptive terms like "car" or "dog" to visuals, achieving near-perfect precision in targeted searches (e.g., 100% for common objects in tested sets).^[1] By providing meaningful metadata, these labels addressed key limitations in early image retrieval systems, where automated methods struggled with semantic understanding.^[1] The game's output contributed to foundational AI datasets in computer vision, supplying labeled images for training machine learning models in object detection and recognition tasks.^[16] For instance, the ESP dataset, derived from player annotations, has been used to benchmark algorithms for multi-label image classification, offering a challenging resource with diverse, real-world web images that require predicting multiple keywords per visual.^[17] These labels influenced early developments in computer vision tools by providing scalable, human-verified ground truth data, reducing reliance on computationally expensive automated labeling.^[1] Research leveraging ESP Game data advanced semantic image understanding, with the foundational paper cited over 3,197 times across computer vision and human-computer interaction studies.^[18] It enabled explorations into accessibility for the visually impaired, such as generating alt-text equivalents for screen readers to describe image content audibly, thereby improving web navigation for users with disabilities.^[1] By 2008, the initiative had generated over 50 million labels across diverse categories, significantly lowering annotation costs compared to manual methods, which can exceed prohibitive expenses for large-scale datasets.^[19] One prominent successor to the ESP Game is reCAPTCHA, developed by Luis von Ahn and colleagues in 2007 as a human computation system that leverages users solving distorted text challenges to both prevent automated spam and contribute to the digitization of books and historical documents.^[20] By integrating into websites worldwide, reCAPTCHA harnessed collective human effort to solve over 100 million CAPTCHAs daily as of 2008, scaling to hundreds of millions daily in later years and aiding projects like the Internet Archive's book scanning.^[20] Within the broader Games With a Purpose (GWAP) framework pioneered by the ESP Game, several CMU-developed games extended its model for specialized image annotation tasks. Peekaboom, introduced in 2006, paired players to reveal portions of an image based on descriptive words, generating bounding boxes for object localization to improve computer vision accuracy.^[21] Similarly, Phetch, launched in 2008, involved multiple players collaboratively crafting full descriptive sentences for images, producing accessible captions particularly useful for visually impaired users navigating web content.^[15] Commercial adaptations drew on the ESP Game's gamified labeling approach for large-scale data collection. Microsoft's PhotoCity, a 2010 GWAP, encouraged outdoor play where participants photographed urban structures to "capture" virtual flags, amassing thousands of images per location to fuel 3D reconstructions in tools like Photosynth.^[22] Academic extensions include open-source GWAP variants adapted for emerging technologies, such as mobile-based image labeling systems that enable on-the-go tagging for citizen science applications like environmental monitoring. The ESP Game's legacy profoundly influenced the rise of crowdsourcing platforms, including Figure Eight (acquired by Appen in 2019), which adopted human-AI symbiotic models for scalable data annotation, emphasizing voluntary or incentivized contributions to train machine learning systems.^[23] This framework, as outlined in foundational GWAP research, shifted paradigms toward integrating human intelligence with computation for tasks beyond traditional programming.^[24]

References

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[PDF] Labeling Images with a Computer Game
Jan 12, 2004 · From the player's perspective, the goal of the ESP game is to guess what their partner is typing for each image. Once both players have typed ...
[2]
Games with a Purpose - Carnegie Mellon University | CMU
The first GWAP developed by von Ahn, the ESP Game displays images to two players who each try to guess words that the other player would use to describe the ...
[3]
A fall spring-clean - Google Blog
Sep 2, 2011 · Image Labeler: We began Google Image Labeler as a fun game to help people explore and label the images on the web. Although it will be ...
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Jun 2, 2006 · The ESP Game is extremely popu- lar, with many people playing more. Games with a Purpose. Luis von Ahn. Carnegie Mellon University. Page 2. June ...
[5]
Rising Star Luis von Ahn Named to Popular Science's "Brilliant 10"
Sep 15, 2006 · The first game von Ahn created was the ESP Game, which paired up players ... 100,000, he notes. "Now, we can get 400 million people working ...
[6]
Google turns to crowdsourcing with image labeler - Ars Technica
The image labeler is based on Carnegie Mellon faculty member Luis von Ahn's ESP Game, which Google has officially licensed. Ahn believes ...
[7]
[PDF] GWAPs: Games with a Problem - FDG 2014
Even after the initial success of the. ESP Game, it was shut down in 2011 [15]. ... Luis von Ahn and Laura Dabbish kicked off the genre of. “games with a ...
[8]
Crowdsourcing Stereotypes: Linguistic Bias in Metadata Generated ...
While ESP has been shown to produce relevant labels, critics claim they are obvious and stereotypical. Based on theories of linguistic biases, we examine ...
[9]
NextSpace : the OCLC Newsletter No. 19
In one four-month period, 13,000 players produced 1.3 million labels for some 300,000 images. Over time, the game attracted 200,000 regular players, and ...
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Security Design in Online Games. Jeff Yan. Department of Computer Science and Engineering. The Chinese University of Hong Kong. Shatin, N.T., Hong Kong. Email ...
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Aug 1, 2008 · The ESP Game, introduced in 2003, and its successors represent the first seamless integration of game play and computation. How can this ...
[12]
[PDF] Streamlining Attacks on CAPTCHAs with a Computer Game - IJCAI
Our work is inspired by the ESP game [von Ahn and Dab- bish, 2004], which pairs two randomly selected online play- ers to create labels for images on the Web.<|control11|><|separator|>
[13]
THE ETHICS OF AI - Power, Critique, Responsibility
Oct 11, 2025 · acquired by Google in 2006 and rebranded as Google Image Labeler. ... consent dialogue affirms the (false) liberalist imaginary that privacy ...
[14]
AI has a culturally biased world view that Google has a plan to change
Dec 2, 2018 · A standard image-recognition system, trained on open-source data sets, can recognize a bride in a white dress, reflecting the classic Western ...
[15]
[PDF] More than just a game: ethical issues in gamification
May 12, 2016 · In ''Framing the ethical issues'' section, we explore a framework for gamification ethics, with a focus on exploitation, manipulation, various.
[16]
[PDF] Human Computation Requires and Enables a New Approach to Ethics
Ironically, human computation provides a potential solution to these ethical challenges. ... von Ahn, B. Maurer, C. McMillen, D. Abraham, and M. Blum, “reCAPTCHA: ...
[17]
[PDF] IMPROVING IMAGE SEARCH WITH PHETCH Luis von Ahn, Shiry ...
Like the ESP. Game, Phetch is an example of a general approach to computational problems, called “Human Computation,” where humans are recruited to collectively ...
[18]
A survey of image labelling for computer vision applications
The ESP game (von Ahn & Dabbish, Citation2004) was one of the earliest examples. At the time, it aimed at providing semantic descriptions “for most images of ...
[19]
ESP-Game - Kaggle
In the ESP game, two players gain points by predicting the same keyword for an image without communication. This dataset is very challenging.
[20]
‪Laura Dabbish‬ - ‪Google Scholar‬
Labeling images with a computer game. L Von Ahn, L Dabbish. Proceedings of the SIGCHI conference on Human factors in computing systems …, 2004. 3197, 2004.<|separator|>
[21]
[PDF] 39 A Game-Theoretic Analysis of the ESP Game - David C. Parkes
In establishing the second point, the authors test a bot programmed with a simple language model learned from the Google Image Labeler, which infers what label ...
[22]
[PDF] Human-Based Character Recognition via Web Security Measures
Sep 12, 2008 · reCAPTCHA: Human-Based Character. Recognition via Web Security ... von Ahn, M. Blum, J. Langford, Commun. ACM 47, 56 (2004). 3. K ...
[23]
[PDF] Peekaboom: A Game for Locating Objects in Images
Sep 1, 2005 · We introduce Peekaboom, an entertaining web-based game that can help computers locate objects in images. People play the game because of its ...
[24]
[PDF] Reconstructing the World in 3D: Bringing Games with a Purpose ...
The result is PhotoCity, a game played outdoors with a camera, in which players take photos to capture flags and take over virtual models of real buildings. The ...
[25]
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Feb 9, 2020 · In this current post, we'll discuss the general guidelines of building a GWAP for some problems. ... Amazon Mechanical Turk. This is a big one for ...
[26]
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Mar 10, 2019 · This acquisition combines the scale, quality and language expertise of Appen's leading global crowd with Figure Eight's innovative data ...Missing: GWAP | Show results with:GWAP
[27]
[PDF] Designing Games With a Purpose - CMU School of Computer Science
Jul 21, 2008 · Two of the most popular. GWAPS—ESP and Verbosity— can be played online at www.gwap.com. ... Luis von Ahn (lav@andrew.cmu.edu) is an assistant.