English-language keyboard (A-Z, a-z, numbers,
punctuation and other basic symbols). When 8-bit ASCII (also called ISO-8859 or
ISO-Latin) is used for books with accented characters like French or German,
Project Gutenberg also produces a 7-bit ASCII version with the accents stripped.
(This doesn't apply for languages that are not "convertible" in ASCII, like
Chinese, encoded in Big-5.)

Plain Vanilla ASCII is the best format by far. It is "the lowest common denominator". It can be read, written, copied and printed by any simple text editor or word processor on any electronic device. It is the only format compatible with 99% of hardware and software. It can be used as it is or to create versions in many other formats. It will still be used while other formats will be obsolete (or are already obsolete, like formats of a few short-lived reading devices launched since 1999). It is the assurance collections will never be obsolete, and will survive future technological changes. The goal is to preserve the texts not only over decades but over centuries. There is no other standard as widely used as ASCII right now, even Unicode, a "universal" encoding system created in 1991.

Project Gutenberg also publishes books in well-known formats like HTML, XML or
RTF. There are Unicode files too. Any other format provided by volunteers (PDF,
LIT, TeX and many others) is usually accepted, as long as they also supply an
ASCII version where possible.

But a large scale conversion into other formats is handed over to other organizations. For example Blackmask Online, which uses Project Gutenberg's collections to offer thousands of free books in eight different formats based on the Open eBook (OeB) format. Or Manybooks.net, which converts Project Gutenberg's books into formats readable on PDAs. Or Mobilebooks, with 5,000 books in Java (.jar) format that can be downloaded from the website to be read on a cell phone. Or Wattpad, a free service for reading and sharing stories on a mobile phone. Once downloaded to your phone, the service gives instant access to works from Project Gutenberg.

As a volunteer, the wisest thing to do is to choose a book published before 1923. It is also required that copyright clearance be confirmed prior to working on any book by sending a photocopy of the title page and verso page (even if the latter is blank) to Michael Hart. The pages should be sent as scans to be uploaded on the website. For people who cannot create scans, it is possible to send photocopies by postal mail. The pages will then be filed, either on paper or electronically, so that the proof will be available in the future, to demonstrate if necessary that the book is in the public domain under the US law. Project Gutenberg doesn't release any book until the book's copyright status has been confirmed.

What is entailed exactly, once copyright clearance is received? Digitization is done by scanning the book page after page to get "image" files. Then volunteers run an OCR (Optical Character Recognition) software to convert "image" files into text files. Then each text file is proofread (i.e. re-read and corrected) by comparing it to the "image" file or the original page of the print version. There is an average of 10 mistakes per page for a good OCR package, and many more mistakes if the quality of the scanner and the OCR package is not great.

The book is proofread twice on the computer screen by two different people, who make any corrections necessary. When the original is in poor condition, as with very old books, it is keyed in manually, word by word. Some volunteers themselves prefer to type short texts, or works they particularly like. But most books are scanned, "OCRized" and proofread.

Contrary to digitization in "image format", which consists only in scanning the pages, digitization in "text format" adds the OCR step: a) the book can be copied, indexed, searched, analyzed and compared with other books; b) it is possible to search the content of the book with the "Find" button available in any browser and any software, without a specific search engine.

The assets of digitization in "text format" are numerous. It makes a smaller and more easily sendable computer file, unlike digitization in "image format", which produces a bulky "photo" file. Contrary to other formats, the files are accessible for low-bandwidth use. They can be copied as much as needed to produce new digital or print versions for free. The typos pointed out after the text is released can be fixed at any time. Readers can change the font and size of characters, the margins or the number of lines per page. Visually impaired readers can increase the letter size. Blind readers can use speech recognition software. All this is very difficult, if not impossible, with many other formats.

If the books released are 99.9% accurate in the eyes of the general reader, the goal is not to create authoritative editions, and to argue with a picky reader whether a certain sentence should have a colon instead of a semi-colon between its clauses.

Project Gutenberg is convinced that proofreading by human beings is a very important step, and that this step makes all the difference. The use of scanned books as is —converted to text format by OCR software with no proofreading— gives a much lower quality result. After running OCR software, the text is 99% reliable, in the best of cases. After proofreading, the text becomes 99.95% reliable (a high percentage which is also the standard at the Library of Congress).

For this reason, Project Gutenberg's perspective is rather different from that of the Internet Archive. In its Text Archive, books are scanned and "OCRized", but they are not proofread. The main formats used are XML, TIF and DjVu. Books are not proofread either in other main collections: Open Content Alliance (OCA), Google Books Search or Microsoft Live Books Search.

Project Gutenberg provides a "Nearly Full Text" search (on the first 100 K of each file) using Google, with a database updated approximately monthly. It also provides a search of book metadata (author, title, brief description, keywords) as a participant in Yahoo!'s Content Acquisition Program, with a database updated weekly. Both are available in the Online Book Catalog (at the bottom of the page). In the Advanced Search, several fields can be filled: author, title, subject, language, category (any, audio book, music, pictures), LoCC (Library of Congress Catalog classification), filetype (text, PDF, HTML, XML, JPEG, etc.), and eText/eBook No. A field "Full Text" was also added as an experimental feature.

On Project Gutenberg's website, a File Recode Service allows users to convert books in one format (ASCII, ISO-8859, Unicode and others) into another, and vice versa. A much more powerful conversion program may be launched in the future, with a conversion into still more formats (XML, HTML, PDF, TeX, RTF), including Braille and voice. It will then also be possible to choose the font and size of characters and the background color. Another eagerly expected conversion is that of a book from one language to another by machine translation software. This may be possible in a few years, when machine translation is accurate to 99%. Still, these books will certainly need some proofreading too by human translators.

4. SHARED PROOFREADING

The main "leap forward" of Project Gutenberg in the last few years is due to Distributed Proofreaders. Distributed Proofreaders was launched in October 2000 by Charles Franks to help in the digitizing of public domain books. Originally meant to assist Project Gutenberg in the handling of shared proofreading, Distributed Proofreaders became the main source of Project Gutenberg books. In 2002, Distributed