I think the two that seem to come closest to what you’re seeking are these:
Callahan, Philip S. The Tilma Under Infra-Red Radiation. Washington: CARA, 1981. seems like it would be mostly scientific data. Don’t know the faith of the author.
Smith, Jody Brant. The Image of Guadalupe. N.Y.: Doubleday, 1983. Specifically says the author is not a Catholic. Says it is an historical and scientific review of the image.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.