Aw. Pity. I don't really see much point in that personally, since people can just as well steal the low-res version... not as if anyone will ever ask you for a full res one to prove your claim; it's obviously your drawing style.
This is really beautiful. It shows that you love drawing her just by the details you put in it and how graceful she is with their ethereal manes and the elements of the night in this. I also love Nightmare Moon. Evil or not, she is a beautiful mare.