[DubaiSis]

I wouldn't stress about what's been done already. A prom picture isn't the greatest idea in the world, but more because it's probably full length and doesn't show your face as well. A nice picture of your face to your shoulders (a head shot), taken outdoors (on a cloudy day is best or when the light isn't too harsh), on a decent enough camera should be fine. Do your hair simply but nice and same for your makeup.

If you have a couple bucks and can afford to get some professional pictures done, that's great, but I know it can be expensive. I'm a fan of having professional pictures taken of yourself from time to time anyway. You never know when you're going to need pictures for other stuff and this is the picture I'd use on your Facebook cover page too.