Luis von Ahn developed the ESP Game , a game in which two people are simultaneously given an image, with no way to communicate, other than knowing the matching label for each picture or the pass signal. The ESP Game has been licensed by Google in the form of the Google Image Labeler.
Players have noticed various subtle changes in the game over time. In the earliest months, through about November, 2006, you could see your partner’s guesses during play by mousing over the image. When the “congenita abuse” started (see below) you could see if your partner was using those terms, while the game was underway. The game was changed so that only at the end of the game could you click “see partner’s guesses” and learn what he or she had typed. “Congenita abuse” was finally stopped by changes in the structure of the game in Feb. 2007 (see below). During the first few months of 2007 regular players grew to recognize a group of images that signified a “robot” partner, always with the same labels in the same order. This appears to have changed as of about March 13, 2007. Suddenly most of the images seen are brand new, and the older images come with extensive off-limits lists.
As of May 4, 2007 there have been fundamental and substantial changes made to the game. Instead of 90 seconds, players now have 2 minutes. Instead of 100 points per image, the score is varied to reward higher specificity. “Man” might get 50 points whereas “Bill Gates” might get 140 points. On August 7, 2007 another change was made. Instead of simply showing the point values of each match as the match occurs, the value of each match is shown next to the matching word at the end of the game. This makes it much easier to see the exact value of specific versus general labeling. A further change was observed on October 15, 2007. The new version was put into place and then seems to have been withdrawn. In the new version you see only the image you are labelling, whereas in the old version the images are collected in the lower part of the screen as you play. Other changes are subtle, for example the score is in green letters in the new version and red in the old. The most significant change is that the clock freezes during the image change, and that time used to be essentially subtracted from the two minutes of play. The changes appear to have gone into full effect on October 18, 2007.
The user will be randomly paired with a partner who is online and using the feature. Users can be registered players who accumulate a total score over all games played, or guests who just play for one game at a time. Note that players come from around the world, some practicing their English, and both American and British English will be encountered (soccer vs. football). When an uneven number of players are online, a player will play against a prerecorded set of words.
The current rules follow. For changes in the rules, see the history section. Over a 2 minute period, the user and his/her partner will be shown the same set of images and asked to provide as many labels as possible to describe each image you see. When the user’s label matches the partner’s label, both will earn points and move on to the next image until time runs out. It is possible to pass on an image but both users must agree to do this. The score is variable from 50 to 150 depending on the specificity of the answer. The 150 score is rare but 140 points will be awarded for a name or specific word, even if the word is spelled out in the image. Terms with low specificity like “trees” or “man” earn only 50 points. There has never been any screening for correctness, so that if both players type “Jupiter” for an image of Saturn, they would presumably both get 140 points.
Labels that have been agreed on by previous users may show on an “off limits” list and cannot be used in that round. Some players think that the game staggers appearance of the images, and that sometimes it takes the first words typed by one player to form an “off limits” list for the other player. In other words, the off limits words may be unilateral, asymmetrical. This would explain the rather frequent circumstance when it seems a partner can’t think of words like “car,” “bird,” or “girl.” Very rarely, at the end of the match it becomes obvious that one image was different for the two players. Perhaps this is simply an error, or perhaps it is a test to see how quickly people will pass when their descriptions do not match, but it may also be a mechanism implemented to view cheaters, if the words for the different images are similar. At times, one user’s computer will fail to load a new image, or continue to display the previous image shown. Times likes these also call for a mutual “pass” on the part of both players.