Here's what I found that works, and it's actually what you are doing, but kinda the opposite: I put a 728 leaderboard adlinks on top, and a 728 leaderboard banner on the bottom under the picture. I have a short caption that labels the pictures (ext. "Russian Army Invades Afghanistan") in at least three places -- the title, in the header, and in the alt text. It's worked like a charm, and this gallery gets me some pretty amazing CTR. P.s. Keep what tytyguy said in mind. You might want to email Google to ask if such a site would be within the TOS. I have seen many sites banned because of putting Adsense ads on gallery sites whose sole aim is to, shall we say, glorify the gift of the female human form, if you know what I mean.
I already mailed adsense several days ago and posted on their google groups. They said its ok as long as no nude/x-rated stuff. Thanks for suggestion.
Some weeks ago i did exactly the same thing you (jackburton2006) said with 2 leaderboards, one on the top of the image and the other on the bottom, but there were very bad results : 6000 PI/day and only about 10 clicks.