I have to agree about the advertising approach - the sponsor links really need to stand out - one site I looked at (a free site) had a red bkgd and black sales text - that text will get skipped right over by a surfer - as the pic thumbs really stood out on the bkgd - change the text to bright yellow or something like that - remember that you are trying to catch the eye of the surfer with your text - not just giving pics away
Look at a Sunday paper with all of those color ad inserts - what catches your eye when you look at them? You are really trying to do the same thing - your free sites are just ads - with a few pics thrown in as filler
another approach is to look at a Hustler magazine or something along those lines - go to the back in the ad section - again - look at what stands out - what catches your eye immediately!!! - actually any magazine ad will work - youve got about 2-3 seconds to make an impression - thats what the sites need to scream at the surfer - they NEED to go to your sponsor!!!