Is there a way to select what you want your adsense ads to be about? I have an image host and dont think people want to click ads for more image hosting if they are already ON an imagehost website.
No.. you can't choose.. you can use section-targeting to focus the attention of the Adsense Bot on certain portions of content, but you can't 'choose'.. You might try the Adsense Referrals - those you can choose and tailor to what your visitors want to see, but they are PPA, not PPC (meaning, they have to buy something, or sign up for something)..
That's the biggest limit of adsense. I have a recipe site, and all i get is other recipes sites ads. All you can do is filter competitive ads, up to 200. On the other side, this will (not so) probably cause a drop in your revenue