Some ads are cheaper, some countries are cheaper. Put 3 ads per page from 3 different networks to counter balance. Then force the page to refresh once or twice. There are many ways to optimize revenues when one really care about revenues.
I hate to break it up to you but your site is picture hosting, it's low engagement and low value. People will not try the wrong "download" button 3 times until they find the right one, only to do the same thing again next week for the new episode of games of thrones.