This is my first instructable, so I hope you enjoy it and it shows you some you didn't know.
I used gimp and picnik, both are free online editing programs.
Step 1: Eyes
I started with the eyes, just because you really can't have a scary picture without changing them.
Depending on the picture quality you may not need too zoom in (control +) to close. Just close enough to see the change in pixel color.
Using the Free Select tool (shift F) outline the eye socket and try to stay in-between the two different pixel colors. Move all the way around the eye and close the loop. You'll know it's closed when the line starts to blink.
Step 2: Filling in the Eye
Step 3: Skin Touch Up
If you choose a pattern and start filling, but you're not feeling the pattern just undo it (control Z). Also, be careful not to double layer the same spot it will just get darker and darker, unless that is what you're going for. Now, that most of the skin is filled get in close and hit those small spots. Don't forget to blur the edges just a little bit and save your work.
Step 4: Black and White
Click on Effects and change your photo to black and white. Now using a brush side of 17 with a hardness of 30% turn your hard work back to it's original glory.
Step 5: Fangs
Step 6: Snake Baby
So what do you think of my little monster, now? Thanks for your time.