After going on a ghost tour over Halloween, several people were able to take photos of ghosts seen through an old hotel window, a few stories above our position. This got me to wonder if this was a trick that relied on the way that the digital cameras may be able to detect non-visible wavelengths, and display them in an image that we can see. I also wondered what type of invisible paint they would use to paint the ghost images that could only be seen by a digital camera. The ghost images look painted, but you can only see them after taking their picture. How was the trick done?