You may find that the photos that you want to repair are in more than one piece. When scanning an old photo with the intention of repairing it you may want to check what your scanner is up to again. See Saving you images correctly. When you scan two bits of a photo you may find that the two halves end up looking completely different. The tones and exposure and even colour may look great on one half and totally different on the other, what is going on?
When your scanner when set to automatic just like a digital camera set to “auto”, it will exposure and correct the image where and how it sees fit. Images with more dark tones in them, may be compensated for and end up lighter and vice versa for light images ending up darker. Colours may even change too.
It is best to set your scanner to manual and switch off all the automatic settings and keep the scanning resolution the same. Turn off the auto tone, brightness, contrast, colour sections and just scan in colour, as basic as you can get. This way both scans should end up the same in their tones and exposures and size. You can then be sure when you are trying to match up the two halves that they will meet easily and make the photo repair simpler too. In fact you can apply this technique when scanning large prints bigger than your scanner. Make sure you scan with around 25% overlap on each scan then this will give plenty to match up when getting your restorer to stitch them together again.
For an updated and illustrated guide see scanning large photos for restoration