That book is Elizabeth Siberry, The New Crusaders: Images of the Crusades in the 19th and Early 20th Centuries. Originally published in hardcover in 2000 by Routledge, it was, just this past November, republished in a paperback version.
About this fascinating, lucidly written, and compelling study, which I very much commend to your reading, the publisher tells us the following:
This is the first comprehensive study of the use, abuse and development of the crusade image in popular and high culture in the nineteenth and early twentieth centuries. Drawing upon a diverse range of sources, mainly from the British Isles, but with parallels from Western Europe and North America, the author shows the different approaches to the history of the crusading movement and crusade images taken by the historian, composer, artist and author.