This is nice! The colors are really eye catching, and I think you've balanced the browns and greens well in the foreground. The pose of the dragon is done well, too, it looks very majestic. :]

The main trouble I'm having is with the photograph in the background. It doesn't quite mesh with the style of the foreground, making the whole thing look kind of tacked on and disconnected, especially since there's no real middle ground. It's cartoon-style dragon, then bam, realistic photograph with nothing in between them to serve as a buffer. I think it would help this piece a lot if the style was consistent throughout. Combining a drawn piece with a photograph is really difficult to make look convincing.

You may also want to consider bringing some of the blue from the sky into the dragon and mountain, in their shadows. Instead of the black shading on the trees and mountain side, it might help to "air" them out a little if you touch them with a hint of bluish grey.