imageColin Berry in part of a comment writes:

Twice now on this site I’ve reminded folk that any difficulty in seeing the TS body image from a distance would have been rendered less of a problem in public displays by the presence (or maybe deliberate addition) of blood stains and scourge marks. So while “over-flagellation” has been cited as evidence of a paying of lip service to prevailing artistic fashion it might equally well have been done to assist visibility, while not compromising the credibility that attaches to a faint body image per se deemed to be a genuine imprint of the body of Christ.

To which Thomas replies:

Nice theory re: blood Colin. I’ve said it before, I’ve got a feeling some, if not all the blood, was added. I still on balance believe the image is ‘authentic’. But not necessarily the blood. Or at least not all of it.

And Colin replies:

Thanks Thomas. It’s in fact quite instructive and possibly enlightening to put oneself in the position of a medieval monk who has been given the task of making a faint body imprint more visible from 50 yards,while (a) doing nothing that detracts from the ghostly body image and (b) can lend further credibility to a 33AD provenance consistent with or reinforcing the New Testament accounts of the torture and crucifixion..

Personally, I’d start with the major blood flows, and not worry too much about some of them seeming to trickle down the frontal hair, the important thing being to leave a signature of the crown of thorns (the latter not being imaged). I’d then add the scourge marks, making them as evenly spaced as possible, with minimal cross-crossing that looks untidy, and trying not to undo my major bloodstain handiwork work by mixing up or overlapping the two types. Forearms? There’s a lot of work gone into creating those intricate blood trails there, so don’t go and spoil it by adding some distracting scourge marks as well, bar the merest hint. I’d also be very careful to keep scourge marks clear of the area on the dorsal side where the viewer expects there to have been long hair reaching down to the shoulders, especially as the latter itself is poorly imaged. Maybe the colleague who did the body image to simulate a sweat imprint felt it best to give the merest hint of a hair imprint, hair tending to trap sweat, perhaps, as distinct from facilitating its passage from scalp to linen.

And BT from Connecticut, where the snow has finally stopped for awhile, writes in an email:

Dr. Berry’s theory is interesting and should be carefully considered. I am inclined to speculate that all or some of the bloodstains were originally there and remain so. I say this because it seems likely and it appears from a very limited sampling that some bloodstains may have blocked image formation. We can not rule out the possibility that well intentioned caretakers of the relic may have retouched the bloodstains. When you consider that the Holy Shroud may be 2000 years old and that it was unfurled before crowds and folded and unfolded countless times the idea of retouching bloodstains becomes plausible.

This is why we need to see the high definition images that church is withholding.

Source of above image:  a clipping from Haltadefinizione image at Sindone.org