There is nothing special about passport photos, just look at the specifications on the state.gov website. The size of the head does matter (look for details too), but it is easy enough to crop it to the proper size.
One hint: I had one rejected for my own passport a few years ago because the background was not white enough. This was the white balance was not correct on the camera. You can even use a white wall in your house to do this - just use the "custom" white balance on your camera to make the wall white. If your camera can't do this, you can correct the WB after the fact in software.
Have the photo printed at CVS for 15 cents, you will get 6 photos on a 4x6. Sizing the image at 900x600@300 DPI works well. Use an X-acto knife to cut it if you are cheap. Just about any photo program can do all of this for you, even most free ones.
QUOTE(slim @ May 18 2007, 10:41 AM)

They recently (well, right before I did the K-1) changed the photo requirements. It used to be something like a side-view 2"x2" black-and-white photo, but now I believe it's a 2"x2" frontal-view color photo. Passport photos are perfect for this. I got the impression they don't have to be passport photos specifically, but they should be somewhat "official" looking. So, if you have a photo that you can cut into 2"x2" square that show's her from the shoulders/neck up, then that should work. I would use a passport style photo just to be sure. Don't have one? No big deal. Have her head to the local photo shop, internet cafe, etc., and have a teenager snap a cell phone pic of her and then have them e-mail it to you. Print it out, voila! As for your (ugly) mug.... head to Walgreens, CVS, your local drugstore, or Wal-Mart, and they can usually make passport photos for you in under an hour.