CAPTCHA, for those of you just joining us, stands for Completely Automated Public Turing test to tell Computers and Humans Apart. Essentially, it’s a challenge-response test used to distinguish between humans and spam-spewing robots. What’s interesting about reCAPTCHA’s implementation is that it’s used for digitizing books.

“Since computers have trouble reading squiggly words like these, CAPTCHAs are designed to allow humans in but prevent malicious programs from scalping tickets or obtain millions of email accounts for spamming,” Google explains in a post to the company blog. “But there’s a twist–the words in many of the CAPTCHAs provided by reCAPTCHA come from scanned archival newspapers and old books. Computers find it hard to recognize these words because the ink and paper have degraded over time, but by typing them in as a CAPTCHA, crowds teach computers to read the scanned text.”

An ingenious idea, crowdsourcing book transcriptions in this way. An effective one too: reCAPTCHA boasts 99.5 percent accuracy at the word level.

Little wonder, then, that Google (GOOG) has acquired it. The company can clearly put reCaptcha’s technology to good use, not just as a security measure, but as a means of improving its own massive book-scanning project.

But that was back in 1948, long before Tamagotchi and Sony’s robotic dog AIBO recalibrated the objects of human affection. And desire. Long before artificial intelligence researcher and international chess master David Levy cast a randy eye on Furby and Tickle Me Elmo and began dreaming up all the lascivious possibilities. Because, according to Levy, within a decade or so robots will be so humanlike in their appearance, functionality and expression of emotions, that we’ll be falling in love with them, having sex with them and even marrying them–Defense of Marriage Act, ahem, permitting.

“It may sound a little weird, but it isn’t,” said Levy, who explores the idea at length in his Ph.D. thesis “Intimate Relationships With Artificial Partners,” concluding that “Love and sex with robots are inevitable.”

Levy argues that there are roughly a dozen basic reasons why people fall in love, and almost all of them could apply to human-robot relationships. “For instance,” he explains, “one thing that prompts people to fall in love are similarities in personality and knowledge, and all of this is programmable. Another reason people are more likely to fall in love is if they know the other person likes them, and that’s programmable too.”

Sounds like a possible new story arc for “Tell Me You Love Me” …

And what of the consummation vows and the marital bed? The human-robot sexual relationship? Silicone “love dolls” have already done some of the heavy lifting there. And there are folks hard at work developing the technology that may someday make coitus roboticus a real possibility. Consider this patent for “Simulated Human Interaction Systems”:

In a simplified form the mannequin or doll could be replaced with devices being artificial versions of human body parts used in sexual activities, for example artificial male or female genitalia as well as or replaced by devices for use in simulating oral sexual activities.

“Most preferably, however, the invention is applied using a mannequin or doll and preferably sensors are provided to be responsive to touch to various portions of the doll, whereby the control system can cause the visual output to correspond but in addition sensors responsive to movement, temperature and pressure and motion can be provided to initiate a physical reaction in the mannequin.”

(Above image courtesy Worth1000.com)