Here is a little how the process of OCR works. Not one of the software products is perfect. You cannot give it a scanned page (picture of a page) and have it output perfectly converted and formatted text. Probably the most widely used OCR software is what Google Books uses to scan books. But if you look at the plain text results many sections are unreadable, usually having to convert words in italics. Definitely Greek is unreadable.
Here is a little about the process of doing it yourself, and doing a good job. 4 years ago I had a book that I wanted to find in ebook format but was not available in that format. The book was about 150 pages so I scanned all of the pages and used OCR. Each scanned page was converted in FreeOCR and the text results for each page copied into an editor. Since I wanted epub format this meant using an html editor. As each page is converted you want to do proof reading to edit/fix/format then while the scanned image is still in front of you. After you have done that with all the pages you then proofread the finished material because you will find other kinds of issues or things you did not find when you proofread individual pages.
This proofreading process is what places like Google Books and Archive.Org do not do when they scan books. So while those sources give you scanned pages (pictures of pages) the text is often not very good. So we now have thousands, if not tens of thousands, of scanned books which were never proofread.