you have to be a best seller. that's how you get on the main pages. you won't know if the image appears or not. the sponsors work like this:
you have a cow, and you want people to see it. so you get the link and now you have the potential at being seen. however 8000 other people also have the word cow, so you will then cycle and maybe be shown at some point in history. the more people that come on here, the less likely you'll be seen.
sometimes the search throws you a bone and it takes something from your gallery and places it on the front page, sort of like a control. and if you get a sale, your rank changes. you'll never know where or when it will happen. but i've found my own work listed on a certain page in google and i was not there at all.
if you have a rare word - something no one else has at all, then you'll have a higher chance at being seen as a sponsor.... however if its a rare word, you'll still be on the first few pages anyway, so that would be a waste of time.
so in the end, it only pays for you to link directly. the sponsors are here to give you hope, but mostly its for the rank of this site with lots of links in. but google is getting savvy and i think those will drop out sooner or later.
best to advertise the site where ever you can, give good keywords, titles and descriptions and rely on google more than the internal search.
---Mike Savad
MikeSavad.com