1. A method performed by data processing apparatus, the method comprising: identifying search event data items for a plurality of identifiers, each search event data item including: information regarding a search event; a time stamp specifying a time and date at which the search event occurred; and an identifier associated with the search event; identifying a proper subset of the search event data items, the proper subset of search event data items being search event data items for search events related to an image search, wherein each search event comprises at least one of receipt of a search query, distribution of search results in response to a search query, receipt of information identifying an interaction with a search result provided in response to a search query, and receipt of information identifying an interaction with a web browser window presenting search result provided in response to a search query; identifying a proper subset of the plurality of identifiers, the proper subset of identifiers being identifiers associated with at least one search event data item for a search event related to an image search; generating, for each identifier of the proper subset of identifiers, at least one image search session data object using the proper subset of search event data items, each image search session data object being for a particular time period and including information regarding image search events derived from the proper subset of search event data items that include the identifier and that occurred during the time period; and generating an image query model using the at least one image search session data object for each identifier, the image query model specifying: images that received an interaction during an image search session for at least one of the identifiers; and for each image that received an interaction, a two dimensional display position of the image on an image search result page when the image received the interaction.