Using the default Frank costume, you must use the special skill move (Y+B) once you've worked up a decent hit counter.
This becomes much easier once you have the first training level done and unlock the melee finisher. Frank will use a chainsaw to spin around and build up the combo faster. I also found that using Y to kick was effective in building up the counter.
Frank will use his camera's flash to stun zombies. Make sure you're in a large group for maximum effect. Frank will first take a photo in front of him, then to the left, and then finally over his right side.
There is an achievement tracker built in for this achievement. You can always look to see how much progress you've made by looking under the progress for the achievement. Good luck!