1. No you're not.

2. They're not allowed to do so without permission.
a. By copyright laws, anything you draw is automatucally your IP in most places.
b. Most sites require you to get permission to post someone elses art (if you're paid, like commissions this permission is usually implied for the buyer)
c. These could be called derivatives. If they try to go all "but I put effort into it" just say you didn't give permission for them to make derivative works either.

I know, I can't stand people that try to defend this kind of thing. I see it a lot around facebook and DA.

I usually let everyone do what they want with my art and characters as long as they let others who they give a copy to do the same thing. In fact I encourage it.