You can fill a region
            of an image with a reference image instead of a colour. The front,
            back, or result image can be used as the reference image. The Wash,
            Shade, Clone, or Reveal media can also be used to perform the fill.
         
         To fill a region with a reference image:
         
         
            - Click Fill.
               The Fill controls appear.
                
- Select the colour model and channels
               you want to work with.
            
- Set the range and softness in the Range
               and Softness fields.
            
- Select the Special Effects medium you
               want to use (Clone, Reveal, Wash, or Shade). See 
                        Using Special Effects Media.
            
- Set the Reference box to Front, Back,
               Result, or Saved, and set the brush opacity.
               A value of 100% fills
                  the area completely with the reference image.
                
- Enable Medium.
            
- Select a point in the area you want to fill.