1. A computer-implemented method comprising: concurrently displaying, to a first user, a plurality of images; displaying, to the first user, a metadata tag; displaying, to the first user, an instruction to select one or more images, of the plurality of images, that are different than the other images, of the plurality of images, relative to the metadata tag; after displaying the instruction to the first user, receiving, from the first user, user input that selects a particular set of one or more images from the plurality of concurrently displayed images; and based on the first user having selected the particular set of one or more images, adjusting the relevance level of the metadata tag to at least one of the plurality of images; wherein the method is performed by one or more computing devices; concurrently displaying, to the first user, a second plurality of images; displaying, to the first user, a second metadata tag; displaying, to the first user, a second instruction to select one or more images, of the second plurality of images, that are different than the other images, of the second plurality of images, relative to the second metadata tag; after displaying the second instruction to the first user, receiving, from the first user, second user input that selects a second particular set of one or more images from the second plurality of concurrently displayed images; and in response to the first user having selected the second particular set of one or more images, adjusting a score, for the first user, based on how accurately the user answered the instruction.