I disagree with this. It would be nice if they would, but it's also hard to impossible to enforce (what do you need a note to be submitted alongside every submission?), hurts the site (it stifles growth, and you have to deal with non-responsive artists), and is quickly and easily resolved by removal and "blacklist" (i.e. you can't post art by these people).
I'm kind of assuming you didn't talk to Lauren Faust or Hasbro about drawing Fluttershy, even that's probably a violation of copyright. I'm sure you'd be happy to remove it if they sent you a note.
Copyright violations are common to ubiquitous online. If they're not making any sort of profit from the art and are willing to remove it when asked, what harm is done? The best thing to do is protect yourself: watermark your images with your name and URL, state in your artists comments that your work may not be reposted. If it really can't be reposted, include a "No reposting" watermark on the image.
no subject
I'm kind of assuming you didn't talk to Lauren Faust or Hasbro about drawing Fluttershy, even that's probably a violation of copyright. I'm sure you'd be happy to remove it if they sent you a note.
Copyright violations are common to ubiquitous online. If they're not making any sort of profit from the art and are willing to remove it when asked, what harm is done? The best thing to do is protect yourself: watermark your images with your name and URL, state in your artists comments that your work may not be reposted. If it really can't be reposted, include a "No reposting" watermark on the image.