About 25 years ago, I first began retouching photos when bleaches and dyes were used right on the photo to retouch it. A very painstaking process to say the least. Today the process is a bit easier with Photoshop but the artistic eye is still key in the results. I believe that to truly restore an old photo, the results should look as if it were the original shot and that nothing has ever been done to it. In other words, "if you can't tell how or where I've worked on it, I've done my job."
I have also been a commercial illustrator for over twenty years. I originally used an airbrush and paintbrushes on illustration board but when I first got a Mac and tried Photoshop, it was not hard for me to replace the old with the new and turn fully digital in my work. Samples of my illustration work can be seen at www.raineykirk.com. There is even a major retouch job for Bridgestone shown under Photo Real that was used as a billboard in Times Square for 5 years. Oddly enough, a representation of that billboard can be seen early on in WIll Smith's movie, I Am Legend.