While a huge amount of material is in the public domain and may be freelyassimilated into a digital library, the most valuable items are recent andprotected by copyright. In order to induce copyright owners to allow theircontent to be accessed or downloaded from digital libraries, mechanisms need tobe developed to compensate them appropriately. In the most extreme case, anauthor might himself produce but a single electronic copy of a work. In orderto justify his effort, he might have to sell it for $100,000. Such a sale wouldbe impossible if the buyer were not able to charge for use of the material, andin fact charge enough to make a profit.
Fortunately, digital libraries theoretically permit precise measurement ofthe use made of content. A secure browser, for example, might prevent copying,printing or retransmission of material. Automated permission systems can bedeveloped whereby users can pay directly for certain kinds of licenses. Thesein turn require metadata concerning the collection of rights the library hasobtained for the item.
However, the implementation of charging requires another paradigm shift. Thecost of building and maintaining traditional libraries is borne by governments,foundations and corporations, but hardly ever by individuals directly. Usage ofmaterials is free, despite the high cost of maintenance. Note that authorsreceive substantial money on account of libraries, because currently eachlibrary that wants a book must purchase a copy of it, and the authors ofpopular books receive large royalties. In the digital world, the following arenecessary to preserve this revenue stream: