Looking for free paint program with clone feature

I have a number of high school graduation black and white jpg photos scanned from yearbooks that have handwritten autographs across the faces that I want to remove. MSPaint does the job, but I have to guess at the shade of gray, and since the photos have a wide range of grays, this is tedious. It would be nice if I could just right-click on the area next to the writing and have this color become the brush fill color.

I've tried Paint25, but I'm not happy with it. Any other ideas?