I saw a documentary last night regarding the Shroud of Turin which made a number of interesting points.
1) the shroud has been dated to medieval times using carbon-14 techniques
2) a demonstration was made showing how the image could be produced using a glass lens and alchemical materials available during medieval times. If true this essentially makes the Shroud the worlds earliest existing photograph.
3) the Shroud is said to contain stitching which was not commonly used in medieval Europe, but was common in Palestine in the first century.
4) blood stains on the shroud are said to be type AB, a comparitively rare type, and to match another fabric sample contained in another church (in Hungary, I believe).
5) another demonstration was made showing how regular bacteria living on everyone's skin would make an image on linen cloth if the body were simply left motionless for 12 hours or so. The body simply needs to be moist, such as from perspiration. The image generated in this way was quite startling.
I personally don't think there is compelling evidence to attribute the Shroud to Jesus. It could be, but it could also be anyone else in the world who happened to die sometime during the last couple of millenia and be covered with a linen cloth. I don't see the blood type as very relevant, because millions of other people had, and have today, type AB. Also, no one knows what blood type Jesus had. I find it interesting that there are no written references to the Shroud prior to the medieval period. Surely, if the early Christian Church possessed this marvelous relic before then, it would have mentioned it?