I would say YES... as your not aligning smaller pictures, there's a space and a border... Don't take just my word on it though
the best way to find out if this is acceptable or not would be contact google...then you could be 100% sure, rather than guessing from the opinions of all of us
there is blog post on official adsense blog. you must read it. url is http://adsense.blogspot.com/2006/12/ad-and-image-placement-policy.html