This was a painful process! Historic photos had to be rephotographed. If the author were lucky, someone else had requested the process previously, and the next author could use the negative to acquire another print. Otherwise, the author had to pay for the generation of a negative and print (as opposed to just the print). And then the author had to pay for permission to use the copy for publication. It could be an expensive and time consuming process. For Comstock Women (1998), I had to obtain a second print of one of the photographs after the book designer decided to use one of the images for the cover. The repository lost the original and the negative, but after several weeks staff final found the image so I could procure another copy.
After the hardcopy print was provided to the publisher (either mailed or hand carried by the author), the art designer arranged for the a location and size of each image on a hardcopy mockup and the entire package was sent to a printer. I do not know by what technology the printer was able to reproduce the image, but there were many substandard processes, and some of my earlier books (i.e. pre-digital) have photographs that don't look all that good. After digitization, of course, everything became much easier and quicker, and the quality improved dramatically.