In Pictures: How to Clean and Retouch Old Photos w...
9. As you work you will need to be careful not to paint with affected pixels from a damaged area. Turn off your new layer’s visibility by left-clicking on the eye icon in the right-hand pane. This way you can remind yourself where the good source pixels are before selecting anything from the background layer.
In Pictures: How to Clean and Retouch Old Photos with Paint Shop Pro