It was originally conceived by Luis von Ahn of Carnegie Mellon University and first posted online in 2003.
[1] On the official website, there was a running count of "Labels collected since October 5, 2003", updated every 12 hours.
At this rate, 5,000 people continuously playing the game could provide one label per image indexed by Google (425 million) in 31 days.
Some other games that were also created by Luis von Ahn, such as "Peekaboom" and "Phetch", were discontinued at that point.
"Peekaboom" extends the ESP game by asking players to select the region of the image that corresponds to the label.
[6] The license of the data acquired by Ahn's ESP game, or the Google version, is not clear.
[7] Image recognition was historically a task that was difficult for computers to perform independently.
When questioned about how much they enjoyed playing the game, collected data from users was extremely positive.
Since the only thing the two partners have in common is that they both see the same image, they must enter reasonable labels to have any chance of agreeing on one.
The ESP Game as it is currently implemented encourages players to assign "obvious" labels, which are most likely to lead to an agreement with the partner.
Ahn has described countermeasures which prevent players from "cheating" the game, and introducing false data into the system.
[9] The choice of images used by the ESP game makes a difference in the player's experience.
The game would be less entertaining if all the images were chosen from a single site and were all extremely similar.
Later versions selected images at random from the web, using a small amount of filtering.