Film and television extras use a color 4"x6" snapshot with a white background, from the waist up. On the back of the photos, you should have the following listed:
Name
Height
Weight
Hair Color
Eye Color
Contact Phone Number
Shirt Size
Pant Size/Dress Size
Coat Size
Shoe Size
Hat Size
On the vast majority of open casting calls for extras, they will take your photo at the casting call. But it is best to be prepared and bring your own photo with several different "looks". One wearing something upscale such as a tuxedo or suit & tie, one wearing something casual such as jeans & t-shirt, and something specialized such as a police uniform. Keep in mind that you should own whatever clothes you wear in the photos in case they want you to wear the same outfit on the shoot. Just make sure that your photos are updated and actually represent what you currently look like.
Click Here for sample photos used for extra work (photos courtesy of Rich Hogan Photography).
Note About Extra Work From Casting Director Lana Veenker:
This is one thing you can do without acting experience, but keep in mind that you can only work as an extra in the region where you live. If there's a movie you want to be in and it's shooting halfway across the world, you need to either move there or have a place to stay for a few weeks (and even then, there's no guarantee you'll definitely be needed). Also, you need to be able to legally work in the country where the film is shooting. The production company won't hire you without a valid work permit or proof of citizenship. Unfortunately, those are the breaks!