A while back I made the image on the left as an experiment in how difficult it would be to make a stencil. It was an extremely entertaining project. The procedure was simple...
First I took a scanned photograph and used IrfanView on Windows XP to convert the image to have only two colors. This can be done straightforwardly, just open the image, and then used 'Image/Decrease Color Depth...', using the 2 color option.
IrfanView does a good job in choosing the correct levels to make a good black and white version of the initial photograph.
Then I printed out the image on a piece of light card...
And then I used a sharp knife to cut out the dark parts of the photograph to create the stencil.
Then using a fabric spray and a white tea shirt, I created a positive image from the stencil on cloth.
I should note that some creativity in the cutting process was required to avoid 'islands' in the image... So you cannot use the image exactly. The light parts (the parts that are not going to allow ink through to the cloth) of the image need to be all interconnected for a stencil to work properly (the stencil needs to be self supporting so all of your light areas need to join). Interestingly, you can be relatively rough in the changes that you make - and I just made adjustments at the cutting stage. The main thing for recognizability in an image of a face seems to be the relative distances between eyes, mouth, and nose - the kind of things that you see as being important for facial recognition in the movies.
All in all, this was a very interesting project - using a simple image processing technique (reducing the color depth to just two levels) to customize a t-shirt. I quite like the result - but I am a little biased I must confess.