Have been thinking about Captchas recently (see below for details if you're not familiar with the term). Namely, are there better approaches to Captchas than digitally altered text? Because there's a possibility that OCR software -- say, the kind that the Post Office uses to read hand-written ZIP codes -- can already defeat the "munged text" strategy.
For example, here's a different kind of image-based approach (I don't have any suitable clip-art handy, so bear with me). Imagine, if you would, that each "bird image" and "car image" -- below -- is a different photo of a bird or car, respectively:
| Bird image | Bird image | Car image | Bird image |
| Bird image | Bird image | Bird image | Bird image |
| Bird image | Bird image | Car image | Bird image |
| Bird image | Bird image | Bird image | Bird image |
Check the boxes underneath the 2 Cars, then Press
My stats are rusty, but I believe the odds that a computer could pick the correct two images (say, cars in this example) is 2/16 * 1/15 or about 1 in 120. Not good enough? Making the user match 3 images ups the odds to about 1 in 600. 4 matches yields odds of about 1 in 1800.
Still not good enough? What if we randomly produce 2, 3 or 4 matches - and force the user to pick all of them? (Obviously, we would change the caption to Check the boxes underneath ALL of the cars). Again, I'm not a stat-dude, but I think the odds now soar to about 1 in a million. I think that's probably good enough. Plus, it relies upon recognition of dynamically chosen images -- not alphanumeric characters -- which requires substantially more computing power to analyze.
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