Google recommends that you put a border around it to seperate the images from the ad. If they find a layout like this they will ban the account. However even with a border some accounts still get banned, but this would be in a case of something like a #efefef border on a #fff background. If you put a border on it you can contact google and a rep will review the page and give you advice, but if you have a questionable border and google finds it, chances are they'll ban the account. This has been my experience anyway.