If you're not hosting your own images, which means you're paying to do so, eventually whatever free site you've chosen is going to pull your images down and you'll have to start over from zero.

 
If you're ok with that, there are tons of services out there that are fine with adult content. Personally, I'd pick a few and spread it out a little, so you're never likely to lose all of your images at once.

Personally, I'd recommend rolling image hosting for your ads into the hosting of your website. Any webhost who's happy to host a provider's site will also be fine with you uploading images and linking them elsewhere. To demonstrate this, I've linked to an image that's hosted on your website below. I'm not sure if your host allows for this, but you can easily find one that does.