Ad and image placement: a policy clarification from the official Google Inside AdSense blog covers issues about placing images next to AdSense units, something that seems to have grown in popularity as a means of encouraging clicks. In short — don’t. Google doesn’t want images to appear related to AdSense links:
We ask that publishers not line up images and ads in a way that suggests a relationship between the images and the ads. If your visitors believe that the images and the ads are directly associated, or that the advertiser is offering the exact item found in the neighboring image, they may click the ad expecting to find something that isn’t actually being offered. That’s not a good experience for users or advertisers.
You’ll find some discussion on Techmeme about the clarification here, and Jennifer Slegg may be along to postscript or link to further thoughts or comments.