Shown below is a photograph of a UFO. The construction of this sort of photo hoax requires combining two photographs. If the original resolution and quality of the two photos are different, then we can detect these differences, even if they are not visible to the human eye.

The color coded image on the right shows the result of our forensic analysis, where the color is proportional to the estimated quality of the image. Note that the region corresponding to the UFO has a significantly different quality (red) than the rest of the image (yellow-cyan).