The site includes a collection of eBooks in PDF format, and they have access to many libraries with source for hardcopy, out of print books. They also seem to be able to use microfiche copies as sources. Sources can go back several centuries.
 How it works
Many of their books have not been digitized yet. They actually digitize the book to your order. When you order a book, their system notifies the library partner that has the book, they pull it, digitize it on a Kirtas Book Digitization System. The book is processed, where they create a Print on Demand copy, and the digital files necessary for Digital Download. The entire process normally takes three to four weeks.
Every book that has been digitized can be downloaded for $1.95US. So every book costs $1.95 + any additional options you may be interested in. For example a book that needs to be digitized has a digitizing fee plus the download fee for an electronic copy. If you want a paper copy then there is a print on demand fee that provides you with a bound copy of the pages. The book can be either a hardcover or a paperback. The cover is usually an image of the original.
You can also pay an additional fee which allows you to share in the distribution of a book that you have them digitize. They will provide you with part of the proceeds if other people buy the book.
 Scan and conversion
A new service is being offered by KirtasBooks. They can now scan paper books as always but they can also convert PDF files to ePUB. See http://scanyourbooks.com/