The author aims to offer for the first time a study of the Shroud of Turin from the point of view of the history of art, intending to show how it was understood, by believers in its authenticity, to be an “artful relic crafted by God” that could be described using conceptual categories from the artistic culture of the time. Today the image of Christ appearing on the Shroud is seen to be paradoxical and contradictory, hence unique, and consequently difficult to investigate by means of art criticism. Here the author proposes that this point of view was not shared by those who saw it and described it in early modernity. Therefore, instead of either ignoring it or emphasizing its uniqueness compared to other works of art, art historians ought to emphasize its connections to the realm of contemporary sacred imagery. Indeed, in describing the Shroud, the artistic culture of Renaissance and Baroque Italy utilized its own interpretive frameworks—not to deny its authenticity (and therefore declare it a mere human painting) but to identify traits of a divine painting, a conscious artistic product by the hand of God using blood in place of pigment. This blood/pigment constitutes at the same time an object of devotion; it is a corporeal relic of Christ serving to depict all his wounds. And this interpretive frame, based on the technical and philosophical speculations on the nature and function of images, is used to describe and explain the origins of the Shroud's image, circulating that concept not just through books, poems, and sermons, but on a practical level through artistic reproductions used for devotion.

This dual nature as image and relic, at the same time earthly and heavenly, is, according to Casper, a quality unique to the Shroud. It permits exploration and veneration of all the bloody wounds from the passion of Christ as a “fifth gospel” (on which, among others, Cardinal Carlo Borromeo based his devotional practices). The Shroud enabled one to imagine the blood exiting the body of Christ, and at the same time to adore it similarly to the eucharist, whose devotion was greatly advocated by Counter Reformation theologians.

A careful analysis of sixteenth- and seventeenth-century texts shows the repeated use of familiar artistic terminology, where Deus Pictor acts as an inimitable artist with a skill superior to any human painter. Artistic theory combines with theological explication, intent on using the Shroud as tangible proof of the Resurrection of Christ. For various authors concerned with reconciling the theology of Christ's blood with the Shroud, Christ's revival in the tomb happened in such a way that the body only partially reabsorbed its fluids. God, acting as a painter, had the image form out of the blood left behind, and distributed accordingly when the body of Christ came back to life. The result is what Casper defines as a “subtractive painting” and a “painted byproduct of the Resurrection,” emphasizing that “crediting the Shroud's formation to an artful resurrection originates not in religious theology but in art theory” (79). Caravaggio's famous Deposition (1604), according to the author, aligns with and visually represents these concepts. As a result, the Shroud got conceived not just as a painting of the passion, but also as a product of the resurrection and proof of the victory over death.

The final two chapters focus on painted and printed copies of the Shroud. Some of these were reproduced on cloth, often at full size, and were capable of replicating as faithfully as possible the qualities of the original (the oldest surviving one is from 1516). Others were prints that showed the public displays of the Shroud or the Shroud alone, and functioned as souvenirs for private devotion or as visual aids to meditation printed in the pages of books devoted to the relic. According to the author, despite variances in material, style, and even size, these copies together constitute a cohesive group distinct from other representations of the Shroud—such as those that show the relic within historic scenes or narratives. Regarding the full-size copies on cloth, they do not get read through the interpretive lenses of our times that disqualify them as forgeries or pale imitations of an original, but rather as copies able to achieve a certain equivalence with the authentic Shroud. For this too the painter of a copy sometimes completed his work while kneeling with head uncovered and surrounded by candles and praying priests. After completion the copy was then placed in contact with the original (just as had happened in older times with brandea, objects that got touched to relics) and could be themselves treated true relics. Often these copies were sent by request to rulers, princes, ambassadors, and church dignitaries.

Casper pays particular attention to an early seventeenth-century, full-size cloth copy kept in Rome at the church of Santissimo Sudario dei Piemontesi and inserted among the architecture above the main altar. This is a unique setting for two reasons: because the church was the religious focal point for the community of Savoy subjects in Rome, and because this is the only copy at that time put on permanent display at the altar of any church. Despite being a simple painted representation, matching the form and appearance of the original Shroud of Turin but deprived of its miraculous qualities, this copy takes on a singular role of a relic and icon simultaneously. This is what allows it to be installed in a sumptuous baroque altar complex as if it were an actual relic.

After reading this book one can only be grateful to Casper for having examined the relationship between the Shroud, art, and theology so well from a perspective that is unique, rarely encountered, truly innovative, and fully grounded in the sources. Particularly praiseworthy is the richness of its bibliography and the unpublished material consulted, especially that in Italian, the author's knowledge of which is absolutely impressive and is always treated with precision and expertise.