Good news. There is an online tool that will help you do just that. Visit http://flashface.ctapt.de/.
Here is a sample. Tried to come up with a sketch of this fiftyish male who, together with a younger partner, rides jeepneys from Visayas Avenue to Mindanao Avenue or Edsa, during the morning rush, and victimizes unsuspecting passengers by slashing their bags. I happen to take the same jeep with them almost once or twice a week.
The sketch is quite off but it is probably because I am poor at recalling faces. Try the application yourself and see if you can come up with an accurate sketch.