Methods, systems, and apparatus, including computer programs encoded on a computer storage medium, for selecting thumbnail images to display with text advertisements. In one aspect, a method includes identifying landing page non-textual content items from a landing page to which the textual content item links and which a user device requests when the textual content item is selected at the user device; for each landing page non-textual content item, determining a relevance measure that measures the relevance of the landing page non-textual content item to the content of the landing page; selecting one or more of the landing page non-textual content items for display with the textual content item based on the relevance measures of the landing page non-textual content items; and storing, in a data storage system, data associating the selected landing page non-textual contents with the textual content items.