The video above is not very exciting unless you take a camera set to F4.5 and 1 sec exposure and take pictures at the appropriate times in the video. Basically, by using a long exposure, the camera is able to add up a set of frames that together form an image. Only by looking at these summed up pixels can you see the image hidden inside. I tried it and it works pretty well. I think it is an interesting form of encryption.
I encourage you to try it for yourself, but if you don't have access to a digital camera with manual controls, you can see the effect here.