In Pictures: How to Clean and Retouch Old Photos w...
5. We will use the Clone brush to copy unblemished areas of our original image on to imperfect areas of the layer we created in Step two. Your new layer is above the original layer so it will cover up the scratches as you work. If you make a mistake use Ctrl-Z to go back a few steps or right-click on the layer to delete it and start again.
In Pictures: How to Clean and Retouch Old Photos with Paint Shop Pro