Equal Playing Field
Make sure each group has a similar camera. Decide if you want players to use Polaroid film, digital cameras or phone cameras. Ensure that each team has similar access to transportation if the hunt requires them to travel around town. Give them your phone number so they can call you with questions.
Designated Photographer
In a photo scavenger hunt, someone has to hold the camera. Decide how you want players to handle this. One solution is to select an additional person to accompany the group for the sole purpose of taking pictures. Make the game more challenging by requiring that groups recruit a different stranger to take each picture, getting the signatures of each stranger as proof. Or mandate that no one can help the group take pictures, which would require group members to balance the camera on surrounding objects or somehow acquire a tripod.
Creative Instructions
It's easiest if the groups have all the picture-taking instructions ahead of time, but it can also be highly entertaining if each instruction is a clue that leads to another. You may want to assign each photo a point value, giving more challenging photos a higher number of points. The team with the most points --- not necessarily the most photos --- wins.
Post-Game Slideshow
After all teams complete the hunt, showcase the photos so everyone can have a good laugh. If you used digital cameras, arrange to download the pictures to a computer or use a television equipped with a memory card reader. Import the photos and play them as a slideshow. If you used Polaroid cameras, prepare a wall where each group can post its photos. Organize the wall photos by group or by task. Award individual photos prizes, such as "Most Dangerous" or "Best Blackmail."