Google has publicly published what is and isn’t allowed in terms of image placement next to Adsense ads.
A simple summary — don’t place images that make an ad look like site content or navigation. This little trick has made publishers millions of dollars and is particularly common in Myspace layout sites, game sites (flash & web based), Photoshop tutorials, and the list goes on.
Another clarification Google has stated — “What if I place a space or a line between my images and my ads? Would that work? No.”
This official statement on Google still leaves room for interpretation, or the “grey” area as Shoemoney would say. However, Google’s image examples of what isn’t allowed sends a clear message of what you are not allowed to do (click blog link and scroll to the bottom to see.)