A British company called Faber & Faber is doing print on demand books with a wrinkle: each book has its own distinct cover that's generated at print time.
Generating the borders was just one, if major, task of the final solution, though. The custom software written in Processing, straight Java and PHP works as an internal webservice at Faber which receives new batch orders and then generates complete, print ready PDF files with all copy, branding, spine, ISBN, barcode and optional high-res JPG preview using the book details supplied. Generating a single cover only takes about 1 second, but due to its iterative and semi-random nature can sometime require hundreds of attempts until a "valid" design is created which is judged to be "on brand" by software itself.
What a day it will be when software can determine whether all of us are "on brand" or not. (thx, david)