Recently my mother found and old photo of her she wanted me to restore and print for her. Oddly I had a copy of this photo already, but it was a scan of a photo copy I used in the title credits of the film so when I had the chance to work from a much higher resolution scan of it I was really happy to do it.
For years I worked with PBS on a few American Experience episodes (won 2 Emmys and a Peabody Award on those projects yet somehow haven't had any more work from them in years) restoring and animating images and I LOVED doing it. This little thing for my mom made me realize how much I love to bring back old photos to their former glory.
I could have taken this even further but there is a point where only I will ever see the work I did in the restoration. I have a very precise series of steps I do when restoring something. I start fixing the largest problems first which are usually tears and missing body parts. If I have access to other photos from the same period of the same person, I can usually replace a hand or arm or eye, there are limits of course. I will then clean up the dust and stains, by hand. If there are big black sections with dust and scratches I might selects only the black and run a dust an scratches filter to save time, but only in areas of solid black.
Lastly I will convert it to black and white (if the photo was in B&W to begin with of course) and then add back in the sepia tone if the client wants it.