Thanks for pointing this out! I always prefer if people ask for permission before using my images, but since the artist did credit me in the description, I say no foul on this one.
But the pony community has really been one of the most considerate fandoms I've ever worked with or taken part in, on the subject of art theft. I've found some of my other fandom stuff ripped off on other sites often enough to give me a bit of a twitch on the subject, but bronies have been unique in the artists and the communities really seeming to make an effort to prevent theft, or point it out when it happens so it can be corrected. I appreciate the hell out of it.
Sorry for the rambling reply, this is just one of my favorite outstanding things about the community. <3