Since I'm into genealogy, I do quite a bit of work on restoring old photographs from my family connections. This has also turned into a small revenue stream when I do it for others. I say "small" because few customers realize how long this kind of work can take, and, when I give them an estimate from my hourly rate, they tend to settle for a scan, without any restoration. Seems great-great-grandma's photo wasn't worth that much to them after all. If you click on Restoration under the Categories listing on the right, you can see we haven't had a restoration tutorial for over a year, so it must be time to talk about it again. Whole books are written on restoration, so, to keep this short, I'll hit the highlights. Drop me a line with more questions if you get stuck.
Keep in mind, there are many other ways and subtleties in each step. I recommend you try lots of things to find your own method; my method keeps the per image time to a minimum and produces a file I can give to the client. If you search the Web on this topics, you'll find lots of other methods. The bottom line should be whether the end result is better than the source photo.
Start with the best scan you can get. Save the file as a TIF. Until you know exactly how your scanner and capture software work, you should probably make multiple scans, varying the settings.
Many times the source photo is very small. You'll probably want to print it in a larger-than-original size, and I've found that you can do this in the original scan software (look for something that says "target size"). Your file size will grow quickly as you scan for a target size larger than the original size, but the extra pixels will come in handy later. (At this point, I import the scan into Lightroom.) The high resolution scan almost always, however, creates an immediate problem.
High resolution scans often show a Moire pattern, an annoying artifact that has a long, technical explanation we won't go into here. Regardless, it shows up as a repeating pattern in your high resolution scans, and that means more time in post-processing. You can scan at a lower resolution, but you also lose some flexibility that you have with higher resolutions and larger file sizes. If your scanner software has a Descreen setting, it usually reduces the Moire. I've annotated the 2x3 original so you can see the problems after the scan. You can see the Moire pattern clearly in the 100% view below the original.
To fix this issue, you need a program that can manipulate pixels. If you're like most folks, you're using a version of Photoshop (Elements, CS, or CS Extended). The first step is to make a new layer. On the new layer, you navigate to Filter/Noise/Median. The only adjustable factor in Median is Radius, and you should keep it is as low as possible (very low single digits) because this action blurs the image. The effect is affected by the size of the image (remember, I told you to opt for the higher resolution and larger file size?). With large images, minor changes in the Radius numbers don't cause as big an impact as they do on small images. Larger is better.
If you have details that cannot afford to be blurred, like eyes and the brass on this soldier's uniform, you can add a mask to the blurred layer and paint with a black brush to prevent the blur. You'll probably have to spend some extra time, later, on the masked items since they will still have the original flaws you were trying to eliminate. You can see my mask below. I've used a full black brush for the critical details and a much lighter brush (about 30% opacity in this example) to keep important edges fairly sharp.
At this point, you go to Image/Image Size and resample your image (smaller). I keep the image as large as possible, but the settings vary for each image, so try several settings until you're happy with the results.
For damaged photos, you've finally reached the retouch/restore point. Add a new blank layer, and set your Healing Brush and Clone Stamp to sample the "current and below" layers. We've explained this in earlier blogs. The blank layer provides a safety net for you if you make mistakes in your work or want to close the file before you're actually finished.
Zoom in as far as you need to, so you can see the details closely. This part of the job can be very tedious as you fix tears, scratches, stains and the remaining Moire left when you masked fine details. I usually zoom into 200-300% view and, starting from the top left, work my way down and across the image. This method ensures I don't lose my place during repairs. I don't have any other tricks to speed you through this step. Here is where you can easily spend a couple of hours working to fix all errors and repairs. Put on some good music and take frequent breaks.
Finally, add back some sharpness with Filter/Sharpen/Unsharp Mask. And, since old photograph colors are usually faded and dull, you can add a Levelsadjustment layer to bring back the original colors and add vibrance. When I'm finished, I save the image, and Lightroom adds it to the library. (You can skip the last step and fix the color and vibrance on the repaired image in Lightroom, if you prefer that tool.)
Here is the original scan and the finished work.
Give it a try. The first one will take some time, but keep working until you have your own method down. The more you do it, the easier it becomes.