It's pretty easy to do. The part the took me longest was getting my stupid to printer to work and choosing a picture that looked good contrasted.
This is the first time i have done this and i messed up a bit. but i'll do another soon and take you through the steps. and I'll actually put it on canvas. im out of it currently and i did this on carddboard
And right now the stupid uploady thing isn't working so I can't put actual pictures up. I will soon.
Pick a picture out of your pictures and turn it into a greyscaled one. Then play with the contrast and brightness. Make it look similar to this once your contrast and brightness adjusting is done.
Print your picture out and then cut out either the black or the white parts. whichever is easiest. This will sort of create a stencil.
If you cut out the black parts, make sure the white parts are still completely connected and not cut up, and vice versa.
Tape your pieces onto your canvas where they are suppose to go. Make sure no tape is showing where you will be actually painting. This will mess it up.
Paint over with black or which ever other color you choose. make sure that the paint doesn't go under the stencil. Then let it dry and pull off the paper pieces.