It is not so simple. The characters are not the same colour as in the image. Look at the eyes and the nose for example. It seems to be doing a more advanced kind of image feature detection.
It is, just the white pixels on the image are black text on the poster, and the same with black pixels, so Gopher's eyes (and the other black parts) disappear.
There is a Light Text option, with that white pixels are grey so you can see the eyes :)
It's a great idea btw.