Yep,
Look up and split test the top three tattoo sites on clickbank, I've heard they take a lot of clicks to convert but they do convert - People usually just look up designs/tribal lines/print them out for ideas etc. so turning them into buyers would be hard i think. You can also offer or make a collection like the clickbank ones and offer it for free in turn for whatever (fill out a survey, opt-in to x...), or just sell the inventory as suggested.
How much traffic does it get (daily uniques)? and where are they from, and how long do they stay? If you can profile your traffic a bit you should be able to put together nice pre-sells and warm up your buyers easily for the tattoo ebooks... Don't 'just' put a banner or two up, actually endorse it, review it/a few/recommend one, and softsell, you should be able to pull much more than you are from adsense.