stains

How do you get a stain off your picture ince you scan it on the computer? Can you?

That sounds like a job for the Cloning tool, sometimes called the Rubber Stamp Tool, sometimes called the Clone Stamp Tool.
Whatever your version of PS calls it, you can use it to copy non-stained portions of your image and "paint" them over the infected areas. Find part of the image that you want to "clone". Hold down the Option/Alt key and click there. Then move the Cloning Brush into postion and start painting! The tool functions like any painting tool with options for opacity and brush size.

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