Why not both? Why would their greed have a limit like that?

I could see this being a very interesting watermark - the free demo is sponsored by Coke, and all images will prominently feature the product. Upgrade to a paid/business/Enterprise account to get images without the product.

Given how many God-awful advertising patents have already been filed, I really can’t see anyone turning down this opportunity. The only reason against it would be a technological limitation- making sure the product isn’t featured alongside negative/toxic content. For instance, Hitler yelling at a bunch of homeless orphans (while holding a Coke)