matrix_jan - 6:01 pm on Mar 9, 2012 (gmt 0)

It's a common design solution to have an image(height:90px) on one of leaderboards's sides. It makes the page look "whole" and doesn't scare users. As long as the image is at least 20px far from the ad and the image doesn't encourage users to click on the ad, google is fine with it. It's up to you.

https://support.google.com/adsense/bin/answer.py?hl=en&answer=48182