Suzi and others, I love to discuss the Shroud with anyone who is interested because I have read about it and collected articles on it since the 1980's.  I also was blessed to attend two large conferences: 2001 in Dallas, and 2008 in Columbus, OH.  I think it's great that people can believe without the Shroud, but I believe I needed it to return to the faith of my childhood.  Science courses in college had really caused me to question everything.  Jesus gave Thomas physical evidence when he requested it, however, Christ said it was more blessed to believe without physical confirmation.
 
The face cloth that you were talking about is the Sudarium and it is well documented that it has been in Spain since approximately the year 700 A.D.  It has the blood, but not the image.  This doesn't necessarily mean that it was not on Christ's face at the Resurrection.  There is a theory that the linen in the Shroud, went through a process that developed special type of chemical film (similar to a sugar molecule) on the surface.   When the power of the Resurrection bombarded these molecules with energy (neutrons?) they changed color and created the image.  I think you can find this explained better on www.shroudofturin4journalists.com.  The material in the face cloth had not been processed in the same fashion, so it did not develop the image.
 
Here are two other theories that I find most fascinating.  You can research them further on www.Shrouduniversity.com. (Click on the Ohio State Logo).  Dr. Petrus Soons believes he has identified a raised area under the chin of the man of the Shroud.  After enhanced digital techniques, he believes that it is a sign that reads "lamb" in Aramaic.  You can hear him describe it and see photos on this website.  It is about 27 minutes into his presentation.  If Christ was mocked as king, He could have also been mocked as a lamb since John the Baptist referred to him as such.  Since it was passover, I don't think it unreasonable to assume there were lamb signs in Jerusalem.
 
The second theory explains how the blood on the Shroud could have retained its red color after all these years.  On the same website, I believe, you can find a presentation of Italian scientists who bombarded human blood with neutrons.  The bombarded hemoglobin formed a stable compound that remained red.   
 
Since I am a medical technologist who works in a hematology lab and a blood bank, these studies are fascinating to me.  I hope some of you also find them fascinating and faith inspiring.   bc