Have you started seeing images in online reCAPTCHAs that look suspiciously like house numbers pulled from Google Street View? Well, as it turns out, that’s exactly what they are. Google confirmed it’s currently running an experiment that involves using its reCAPTCHA spam-fighting system to improve data in Google Maps by having users identify things like street names and business addresses.

reCAPTCHA, for those unfamiliar, is the system originally developed at Carnegie Mellon University to improve upon the use of CAPTCHAs (aka, the “Completely Automated Public Turing Test To Tell Computers and Humans Apart”) – it’s the distorted text meant to stop bots from signing up for online accounts. The reCAPTCHA technology was acquired by Google in 2009, and if you use the web, you’ve definitely used it before. It’s what puts those security questions on websites that ask you to identify the words and numbers in the pictures displayed to verify you’re human.

The system is designed to cut down on spam and fraud, but it also helps digitize the text in printed materials, like books and newspapers. Google has been using reCAPTCHA to digitize content for Google Books, for example, as well as for the Google News archives.

Over the past few days, however, some users have been seeing another type of reCAPTCHA appear – photographs. The new reCAPTCHAs present an image where one side contains the warped text users are familiar with, while the other side shows a somewhat blurry (as if zoomed in) photo of numbers. The numbers are clearly street addresses, which has led to some speculation that Google was pulling these from Google Street View.

One place where this new reCAPTCHA has been known to pop up is on Google’s AdWords website, and specifically on the page hosting the keyword tool. You won’t always see this new reCAPTCHA, though – I refreshed this page a dozen or more times this morning, for example, and still couldn’t get it to appear. Your mileage may vary.

The above image is one example of what the new reCAPTCHAs look like.

A larger collection of these images also recently appeared on the Blackhatworld forums (below):

According to a Google spokesperson, the system isn’t limited to street addresses, but also involves street names and even traffic signs. We haven’t spotted any of those other types in the wild, though.

Says Google:

We’re currently running an experiment in which characters from Street View images are appearing in CAPTCHAs. We often extract data such as street names and traffic signs from Street View imagery to improve Google Maps with useful information like business addresses and locations. Based on the data and results of these reCaptcha tests, we’ll determine if using imagery might also be an effective way to further refine our tools for fighting machine and bot-related abuse online.

Although many users are just now noticing the new images appear, Google says the experiment actually began a couple of weeks ago.

Image credit: Ian for the top photo; Blackhatworld user “dirtbag” (heh.)