There’s an initiative afoot to kill two birds with one stone: secure websites and get a book written in the process.  Here are the details from CNN:

Researchers at Carnegie Mellon University have discovered a way to
enlist people across the globe to help digitize books every time they
solve the simple distorted word puzzles commonly used to register at
Web sites or buy things online.

The word puzzles are known as
CAPTCHAs, short for "completely automated public Turing tests to tell
computers and humans apart." Computers can’t decipher the twisted
letters and numbers, ensuring that real people and not automated
programs are using the Web sites…

Instead of wasting time typing in random letters and numbers, Carnegie
Mellon researchers have come up with a way for people to type in
snippets of books to put their time to good use, confirm they’re not
machines and help speed up the process of getting searchable texts
online…

Many large projects are under way now to digitize books and put them
online, and that’s mostly being done by scanning pages of books so that
people can "page through" the books online. In some cases, optical
character recognition, or OCR, is being used to digitize books to make
the texts searchable.

But von Ahn said OCR doesn’t always work on
text that is older, faded or distorted. In those cases, often the only
way to digitize the works is to manually type them into a computer.

Von
Ahn is working with the Internet Archive, which runs several
book-scanning projects, to use CAPTCHAs for this instead. Internet
Archive scans 12,000 books a month and sends von Ahn hundreds of
thousands of files that are images that the computer doesn’t recognize.
Those files are downloaded onto von Ahn’s server and split up into
single words that can be used as CAPTCHAs at sites all over the
Internet.

If enough users decipher the CAPTCHAs in the same way, the computer will recognize that as the correct answer…

Von Ahn approached the Internet Archive to get help in developing the
new system, but it has not been put into use yet. Theoretically, von
Ahn said the new book-based CAPTCHAs could be used in place of any
CAPTCHA currently on the Web.