Did the blood go on the Shroud before the images?
There is no image beneath bloodstains; the blood interrupting the formation of an image. As reported in two peer-reviewed scientific journals, (Heller, J. H., Adler, A. D., Applied Optics, 19, 1980, pp 2742-4 and Heller, J. H., and Adler, A. D., Canadian Forensic Society Science Journal 14, 1981, pp 81-103) when blood within a part of an image (containing porphyrin, bilirubin, albumin and protein) was dissolved, there was no image beneath the blood. However the images were formed, bloodstains blocked the process immediately beneath the blood.
If a faker of relics had created the Shroud, either by painting the images or by some medieval proto photographic technique, he would have needed to apply the bloodstains first and then carefully create the images around them. This would be particularly difficult if the image was formed by some proto-photograph method.
If image formation was a natural chemical reaction, as is now widely believed among serious Shroud researchers, bloodstains would have blocked the process. While this doesn't particularly add credence to such a hypothesis, it is consistent with it.