I wanted to send my family tree to my sister. After testing to see if the 'RelativePath' reference in the XML would actually be used, I discovered it wasn't.
If the FullyQualifiedPath isn't set on my sisters machine, to exactly the same as my user directory, she won't be able to see any images (ie in the 'Images' folder).
 
I created a patch for this, which needs rework in terms of design, but it works. I can copy/paste my Family.Show folder to anywhere on my hard drive, including xxx.family one level outside that folder.
Then I can browse and open that file and have Family.Show be able to find the photos (using the RelativePath).