What You'll Need:
Picture of Choice
Marker or Pumpkin Poker
Step Two: Remove Colour by Adjusting Levels
Those who are fortunate enough to have Photoshop, this is a much easier step. (http://www.howtogeek.com/howto/33143/how-to-create-a-pumpkin-carving-stencil-in-photoshop/) But even the most basic of applications and programs that are native to Windows and OS X can easily handle what we need it to do.
Windows: Windows Live Photo Gallery
Windows Live Photo Gallery is amazingly versatile with a lot of picture editting options. Once you have your image of choice open, select Fine Tune from the top and adjust the exposure and color. The Yellow Filter Effect works well to start the process although that's just a personal preference of mine. The point is to remove all trace of color while keeping the lines strong and the bulk of this lies in the exposure options, setting the brightness, contrast and shadows as high as possible without losing the important details. What we'll be left with is the black and white image (with at least some minor shadowing which we can ignore.)
Mac OS X: iPhoto
The iLife compilation is fantastic for all things photos, movies and music creation and it's the next step for Mac Owners. The same array of options that are on Windows Live Photo Gallery are available via iPhoto. Under edit, we start with the quick fixes such as cropping and straightening out the image. Afterwards select the Black and White effect and adjust the light and darkness to even out the image. The adjust menu is our best friend here to get the image perfectly balanced. Once again the objective is to get a black and white image with as little shadow or shading as possible.
Now that our image is ready, it's important to remember that the image has to be sized correctly. The option to resize exists in OS X's Preview (Tools > Adjust Size) and Windows Live Photo Gallery (resize photo under the Preferences menu under the Edit tab). We don't want a small face on a big pumpkin or vice versa.
Step Three: Edit and Refine
Now that we have our black and white image, we need to make sure that the image is ready for the pumpkin by closing up some lines. Otherwise our jack-o-lantern would just look like a blobular cut out. The trick is to imagine that the black and white are reversed since the black here is what will be glowing in the darkness. There can't be any contained islands of white nor can it be too enclosed that it'd break off during the carving process. Keep it aesthetic and efficient.
For Windows, Paint is the next place to go. We don't require a lot more other than to remove some lines or spots that might compromise the overall template. Unfortunately there is no native Paint App for OS X, however with access to the App Store there are a few helpful numbers that can assist us. Since we don't need any extensive features, the basic version of SketchBook Express allows us to pull off the same result as Paint.
Step Four: Print and Cut Out
Once we have our print out, it's time to apply the template to the orange canvas. There are two options from this point on. Cut out the black lines out and then stencil the design onto the pumpkin in marker or tape the print out onto the pumpkin and prick the carving lines with a poker.
After we have our lines properly set up on the pumpkin the next stage is carving. There are a lot of guides online to help with the carving process. From there it's an entirely new endeavour. Good luck and happy carving!