Graphical ads in various formats. (View the ad formats page on the AdSense Help Center.)
Like text ads, Google's image ads can be contextually targeted to the content of a publisher's webpage or placement-targeted by advertisers who run pay-per-impression campaigns on specific content placements in the AdSense network.
Running a combination of image and text ads expands the available ad inventory for your site and offers increased revenue potential. Google's technology determines on a page-by-page basis whether text ads, image ads, or video ads are likely to make you more money, and serves the appropriate format to your page.