Help?

Okay, so this isn't quite icon related, but I'm having a problem and I wasn't sure where else to go for help, so hopefully ya'll don't mind me posting this here.

I'm having a problem saving images, almost every time I right click an image and try to save it, it saves as a .bmp image. It's about to drive me nuts, and I don't know why it's doing this, or how to fix it. So, if anyone could please help me and tell me how to fix this, I'd really appreciate it.

Thanks