Ooh, it is not impossible to take a photo of mirage.
A mirage happens when a bunch of rays of light take a detour on the way to your eyes -- or your camera. When you look down a blacktop highway, and see a pool of water in the distance, you understand the "water" you see is an illusion. The light rays that create that image, however, are real. Your eye can see them, and your camera can record them.