A lot of people claims the manipulations made from my (or other people's) stock to be theirs. I will soon write a more detailed journal about this issue, but meanwhile, I will at least post this citation from the [link] FAQ:

"How much do I have to change in order to claim copyright in someone else's work?

Only the owner of copyright in a work has the right to prepare, or to authorize someone else to create, a new version of that work. Accordingly, you cannot claim copyright to another's work, no matter how much you change it, unless you have the owner's consent. See Circular 14 [link] Copyright Registration for Derivative Works."


The highlighted facts (most commonly misinterpreted and infringed by DA photomanipulators):

The allowance to use stock images for derivative works and copyright are two different things
You cannot own copyright for a picture/art that was built upon already copyrighted work
Manipulation itself cannot be copyrighted (just like you cannot copyright other things, e.g. names, titles, ideas, concepts, methods...)
You cannot disallow people to copy/use your work (just as you cannot do the opposite) of a picture/manipulation that you do not own the copying rights for

Stock usage rules are here. But in short, you can use the pictures for anything you like unless you sell them (make any financial profit out of them). Also please make sure to share the derivative works under the Creative Commons Attribution-Noncommercial-Share Alike 3.0 License. Thank you for understanding!