the game to labels generated by participants that were asked to describe the images. Rules of the game Once logged in, a user is automatically matched with a random partner. The partners do not know each other's identity and they cannot communicate. Once matched, they will both be shown the same image. Their task is to agree on a word that would be an appropriate label for the image. They both enter possible words, and once a word is entered by both partners (not necessarily at the same time), that word is agreed upon, and that word becomes a label for the image. Once they agree on a word, they are shown another image. They have two and a half minutes to label 15 images. Both partners have the option to pass; that is, give up on an image. Once one partner passes, the other partner is shown a message that their partner wishes to pass. Both partners must pass for a new image to be shown. Some images have "taboo" words; that is, words that cannot be entered as possible labels. These words are usually related to the image and make the game harder as they prevent common words to be used to label the image. Taboo words are obtained from the game itself. The first time an image is used in the game, it will have no taboo words. If the image is ever used again, it will have one taboo word: the word that resulted from the previous agreement. The next time the image is used, it will have two taboo words, and so on. "Taboo" words is done automatically by the system: once an image has been labeled enough times with the same word, that word becomes taboo so that the image will get a variety of different words as labels. Occasionally, the game will be played solo, without a human partner, with the ESP Game itself acting as the opponent and delivering a series of pre-determined labels to the single human player (which have been harvested from labels given to the image during the course of earlier games played by real humans). This is necessary if there are an odd number of people playing the game. In late 2008, the game was rebranded as GWAP ("game with a purpose"), with a new user interface. Some other games that were also created by Luis von Ahn,