I remember the original posting of this photo back in the early 2000's on the Ghoststudy forum. The forum and website are still online and can be found here- http://www.ghoststudy.com/ -sadly, the original post is no longer there due to technical difficulties on the website-(along with any of my original posts too!)
If I recall correctly, this was sent in by a member of the forum who lived in Australia and the Grandpa had died over a decade before this photo was taken. The widow of the grandpa had just moved into an assisted living setting and maybe it was her husbands way of letting her know he was there at what must've been a tough time?
(I just wanted to add a personal note; when I've given readings to people who can see my aura/the energy around me, I get told that I have a large white tunnel shape emitting from the crown of my head, so the grandpa figure in the photo also appears as though he is coming from the crown of his widows head.)