It seems to me that an images site should have more color? The front page seems sort of depressingly dull?
Four copies of this graphic on the front page don't help:
Perhaps a statement near the top of the page telling the visitor the purpose of the site would help?
The front page is very large and busy -- and therefore loads very slowly.
Doubling up 728x90 leaderboard ads one on top of the other probably isn't going to help CTR.