If you edit a picture that you didnt take, and put your watermark on it, does that mean it's yours?

I got a picture of lady gaga from weheartit.com, and there was a watermark on it that was pretty much invisible unless you look closely. I posted it on my tumblr, and a few hours later, i get cussed out by the person who edited the picture. I didnt even noticed until after it was pointed out to me. I apologized and deleted the picture, and of course this person didnt respond. my question is, if she didnt take the picture, but only edited it, does that make her the rightful owner?