You may (or may not) be interested in two of the essays in the book Photography's Other Histories edited by Christopher Penney and Nicolas Peterson.
"When is a photograph worth a thousand words?" by Hulleah J Tsinhnahjinnie and "Navajo and photography" by James Faris both discuss work by Curtis, among others.
I love Curtis' work. Thanks for reminding me about the site. I once had it bookmarked but it was swallowed up with all my other bookmarks after a browser upgrade.
One of my biggest regrets collecting photogrpahs was my failure to purchase a Curtis gravure at a very reasonable price from a gallery in Santa Fe a couple of years ago.