Process > Background > Options

Click on the arrow to the right of the Options tool in the Background group to display the following drop-down menu options:  

Create New Image: Put a check next to this option to have Image-Pro create a new image whenever the Subtract or Correct tool is used.  Selecting this option ensures that the source image remains unaffected by the background subtraction/correction operation.  If you uncheck this option, the image of interest will be modified as a result of the background subtraction/correction operation.

Extract Background Image: Put a check next to this option to have Image-Pro create an image out of the pixel values subtracted from the source image.   

Note: For an overview of the background adjustment features, click here.