That's it, I'm leaving.

Okay. I'm sure everyone on this site knows what plagiarism is and that it's ILLEGAL!

A girl who lives across the street from me, used one of my images for her display picture for msn. Normally I wouldn't mind. I typed: Oh, I made that. And she replied: No, I did.
The image is Smile! I had put a watermark on the image but it doesn't matter anymore. She then decided to bring her mum into the matter. I was forced to believe that she created this image when she wasn't even able to explain how she made it.

I am:

1) Not allowed to use it
2) Not allowed to bring up the topic ever again.

Either way. I refuse to believe that she made it, when I'm unable to recreate it.