I've done photo restoration for years and Jerome is right. There are few methods that work on the original. Photos are not like paintings. Once a photo is damaged, it is almost impossible to fix the original like you can a painting. It is usually cheaper and easier to make a copy and do the correction on the negative/new print or on a digital scan using a computer.
Just out of curiosity, what kind of photo is it? Old, new, b&w, color, silver gelatin, inkjet, tintype, etc. Also, what kind of damage does it have?
Because photographic emulsions vary from process to process - it is very difficult to actually do restoration on the original. As Anne mentioned in her post you would most likely get better results (and cheaper) by scanning the original, repairing it in photoshop and printing it thru a good photo lab in your area.
It depends what needs to be done. Tear repair and inpainting are standard paper conservation treatments, more involved treatments usually go to conservators who specialize in that area. A new training program has just started in Rochester I believe.