Dustin Nguyen walks readers of his blog through the process he used to create the cover to Batman: Streets of Gotham #4. Nguyen says he usually works with the writer and editor to come up with a cover design; but for this cover, writer Paul Dini had something specific in mind:
This time around, Paul actually sent in a picture he took of himself holding a knife included with a video clip of an old b&w movie to give the perfect feeling of the characters mood and gestures. it was dead on what we wanted to get across i felt. but still, keeping things open, i tried a few other layouts. none was as effective as paul’s, and i knew it. so i went with #1.
The final cover can be seen here.