Another hypothesis about the image formation process has just been published in a peer-reviewed journal : Forensic Science, Medicine and Pathology : Tattoli, Tsokos, Buschmann, “Could the Shroud of Turin be an effect of post-mortem changes?”
You can have a free access to the first two pages.
http://link.springer.com/article/10.1007/s12024-014-9547-6#page-1
(parental discretion advised)