Don't kill yourself trying to get a professional studio portrait in a suit with gray background, etc. I sent a digital photo that was taken at an airport and it was fine. As long as it's a headshot (not a full body or down-to-the-waist shot), you're not wearing sunglasses, and you're not shirtless or wearing a sleazy shirt, I think the photo will be okay. Grab a digital camera, put on a collared shirt, and go outside with a friend and just have him/her snap a whole bunch of them. (Outdoor photos come out nicely more easily than indoor ones, so my personal take on this is to skip standing against a white wall in your living room.) (you can use a graphics editing program to crop the photo so it's square like a passport photo.) Then email your chosen photo to your school ASAP.
When I started getting interviews, I had already submitted:
1) Transcript
2) USMLE
3) Personal Statement
4) Photo
5) 2 of 4 LORs
Take that digital photo and send it in to your school -- you have plenty of time to do it between now and Sept 1.
When you actually go to interview, some of the programs have their residency coordinator stand you in front of a wall to take a new, "more realistic" photo with a Polaroid. Probably so they can have an ugly mugshot of you along with the nice one you picked out. 😀 Honestly, it felt like a prison line-up, and it's made worse by the fact some of them line you up bleary-eyed at 6:30am to do this.