Artists are using an incredibly creative technique that bring their images to life in a unconventional way. They draw their images which may look somewhat unfinished or discolored, but invert those images on a photo editor such as Photoshop where they come to life. If you're not familiar with photo inversion, it's a filter than turns all the whites to black, the blacks to white, etc. It changes colors to the inverse of the original color. Some of these are just pencil drawings, but when the inverse is created, the results are just spectacular. Just check out how amazing these images turned out.
Inverted art painted on an actual face
Loki from Thor
A monkey in a tie and hat