I looked on all the Instructs tagged with stencil, and not one gives a step by step for making a stencil in my favorite open source photo program The GIMP.
Step 1: Materials and GIMP
-surface to cut on (self healing mat)
-spray mount (optional)
GIMP is an open source raster based graphics editor. It was designed to replace Photoshop.
You can get it here. gimp.org
Install it, open it up, and familarize yourself with the interface for a bit. Done? Good. Isn't open source great? Didn't cost a dime!
Step 2: Pick an image and open your picture in GIMP
I chose a tasteful Stormtrooper sculpture to stencil. Nerdtastic!
Step 3: Crop it
a. GIMP allows you to save a copy in case you want to use the uncropped-unedited image later. Save the copy, then go open the copy in GIMP. (File>Save A Copy)
Step 4: Simplifying the image
a.One way is to go to (Tools>Color Tools>Colorize). If you use this method, you will want to set the Hue and Saturation to 0, and adjust the lightness to fit the image (this can be done to taste, generally you want about an even light to dark for a stencil.)
b. The other (and redundant) method is to go to Filters>Colors>Colorify, and select your color (you'll be selecting white).
Both methods are pictured, I chose to use the filter.