The Spot Healing Brush is perfect for repairing old photographs.
As you can see above, the tool does a remarkable job of not leaving behind
any noticeable artifacts or repeating patterns. The trick is to go slowly and
work on very small portions of the image. Select a spot to fix, and use a
brush that’s only slightly bigger than the selected imperfection. The larger
the brush, the more likely you are to clone unwanted portions of the
surrounding area, and the more noticeable the repetition of pixels will be.