Google is constantly experimenting with new features, tools and visual representations to improve the user experience and usefulness of ads. As part of that effort, they’re currently running a test in which images of specific products offered by an advertiser may appear within some text ads on Google search results pages. This experiment helps users quickly find the products they’re looking for, and offers advertisers a new way to engage potential customers. This feature is currently in a limited beta and only visible to a small number of users on shopping-related queries.
http://www.seroundtable.com/archives/020661.html