"Also, who are these "experts?"
Probably people who are payed by the recording industry to make baseless claims for publicity purposes. This appears to be a publicity stunt staged by
this guy (ironically a rock and roll historian) and the recording industry to make money and sell records and books.
Even if the image is not digital, it can be easily scanned into Photoshop and manipulated. Basically, you take a photo of Mr. Mojorisin himself,
remove the background and select just the body. Then you copy the image of Jim and paste in onto the original photo of the dude at the grave site
(perfectly centered, of course).
Next, you adjust the opacity of the Morrison photo you pasted (which is on a separate layer from the original photo) down to about 20% or so. This
will make the Morrison image appear see through, while not affecting the original photo it was pasted on. Then you add a filter like a motion blur, or
something similar to give a ghostly appearance. And for the finishing touches, you can use the airbrush or smudge tools to give the arms, hands and
other body parts a wavy appearance.
And presto! You have Jim Morrison breaking on through to the other side. The whole process takes about 30 minutes, if that.
As mentioned earlier, the tell tale signs are the ghost image being centered and the photo being of poor quality. The higher resolution and the better
quality photo you use, the more difficult it is to make the ghost image appear believable.