This is not quite against the TOS.. We are not explicitly placing an image next to it.. it is just another ad from another ad provider.. nothing of that sort if mentioned in the Adsense TOS that two separate ad networks can't be kept nearby... at least non contextual ones...
i think better not to place both the advert in the same box.Just play safe and avoid such trick even if it looks nice.
Technically, you arent putting an image next to the google adsense. you're just putting ad code next to it. I dont see the big deal if you want to have 2 types of ads next to each other.. thats just like putting adbrite and widgetbucks side by side.