Image 1   Image 2	Click on these two images to view them at full size and save them to your hard drive or use two pictures of your own choosing. (It's not necessary for one to be darker than the other) Open Image 2 in PI and merge all.  Open the Image 1, click on Ctrl+C to copy it and then Ctrl+V to paste it over  image 2.
	Right click on your picture, select Properties and in the merge dropdown box select Overlay.  Click on OK.
	There you have your new merged picture :-) Should your picture not look quite to your liking then I suggest you open up the properties box again and perhaps try Inverse of Multiply rather than Overlay or perhaps adding a little transparency to your image. When you are finally happy with your results, then right click and merge all.

 

This picture above was done with a cut out obeject (the head and shoulders) and the Inverse of Multiply feature rather than the Overlay.  After the final merge, I then used the smudge tool lightly around the head to smoothen the look.