Another entry in the GIMP tutorials, this one in patching grunge and unwanted doodads within your image. Generally a pretty straightforward process – until it isn’t, and this is intended to head off some of those stumbling blocks that can make things frustrating. Don’t get me wrong; you will still have a lot of trial-and-error, back-and-forth attempts, especially with the complicated repairs, but this may greatly reduce the learning curve.
Something that I forgot to mention within: if you’re not sure about whether you have faint shadows from sampling the wrong portion of a gradient, squinting can actually help this show up better, don’t ask me why. Also, using the scroll bar to jiggle the image up and down or back and forth.
I’ll be the first to say this can get really tedious on badly-damaged images or scans, but I’ve also tried several different shortcuts and have never found one that worked. Don’t rush it – do a little at a time if it helps. But when you see a pristine master image after all your work, it’s worth it.
By the way, all the mildew on this image was taken out in exactly this manner, finding the little spots that were free of it to begin with, and expanding them gradually across the image. I have made 8×10 prints from that restoration, and they look excellent.
Good luck!