The image was not transferred on to the cloth by ordinary methods, ie: paint, blood, makeup, etc. The transfer was not noticed until a photographer took a picture of it. It was noticed first on the negative, not from direct viewing of the shroud itself. When US scientist examined the shroud, there was not any paint transferred on the shroud, nor was any ordinary heat transfering methods know during the 1200/1300AD time period used. Testing by carbon dating has been conflicting since there has been a lot of handiling of the shroud. Some carbon dating put the shrouds age during the 1300's, some carbon dating suggests older some 2000 years ago at the time of Christ. Some scientists are suggesting several possible methods of the transfer. Anything from radiation transfer to chemical. Certain chemicals could have a reaction in an enclosed environment in a sealed tomb on the shroud covering the body of Christ. It is known that there is/was a higher concentration of potassium in the tomb than elsewhere where other people were entomed. Exactly how this could be the reason has yet to be determined. What is intriguing, is that the negative image was unknown by the Vatican authorities until modern photography was used some 800 years later. How would some artist/scientist (DaVinci)even know about negative transfering since photography was unknown back then. I believe science some day will come to understand what did cause this transfer, but for now the mystery will continue. Skeptics wiil continue to call it a fake, believers will continue to believe it is really the image of Christ from the time of his death.