That's a pretty cool idea, but I don't like that it's an added step for the user when submitting a form.

I used to get a TON of spam on my website(s) until I threw in a hidden text field. When the form is submitted I assume the submission is spam if the hidden text field's value isn't blank. I don't get spam anymore and people don't have to mess around with a captcha (plus nobody's complained).

...although I'm sure it's only a matter of time until the spammers figure this technique out.

[The ghurlman response must be a response to the OP, not this comment. This approach is perfectly accessible -- better than any captcha!]

I use the "honeypot" field trick as well, and really like it, but this approach has some problems worth mentioning.

For one, make sure you give real users a way to contact you if they somehow get trapped -- you'd think it won't happen, but have you tested every available form-filler plugin out there? A few months ago Google released a new version of Chrome that started putting email addresses into my hidden field. Maybe Chrome thought it was a "confirm your email" field? No idea; I fixed the problem by adding an HTML label for it. But it's a damned good thing I wasn't just secretly discarding the input, or I'd have lost a lot of purchases.

Next, as you mentioned, if anyone targets you specifically, it's trivial to circumvent this with a single line of code in a bot.

There are ways to make it harder to circumvent, though -- use all random field names, insert the hidden field at random locations in the sequence of fields, etc.. I'm still using the simple approach, though, since it's still working. :)

It looks neat, but fails basic accessibility tests. Blind? Can't use a mouse? You're out of luck.

Read again: he includes a hidden field for the "normal" user (blind or not) and spambots fill that field out anyway and get caught. Pretty clever, but not hard to work around as a spammer if this get widely adopted.

Blind users would have a different sort of HTML rendering mechanisms (screen readers, braille output, OCR, etc) that might make hidden tags visible input unless you somehow indicated to them that the field was a honeypot. I'm not sure on the details, but the concept of hiding a field from the user's view probably doesn't translate very well once you leave the visual rendering arena.

I can't speak authoritatively, but I believe the "hidden" attribute of a field is not a visual cue, it is a presentational cue. In other words, it hides it from all presentations, whether visual, audible, tactile, or other.

"Please leave this field blank:" probably works wonders. Visually impaired users aren't mentally impaired, regardless of what the Upright Citizen's Brigade has taught you.

I have concerns about this. While it is a neat concept and the implementation is impressive, the reality may be problematic. A lot of users may not have the dexterity to accomplish this task with a pointing device, like my Mother. Not to mention anyone with special needs that requires an alternate input device.

Very good point, thanks for the feedback. The full release version will have an option to toggle back to a standard letter-based CAPTCHA.

I would think "bad eyesight" would be more commonplace than people with disabilities that require an alternative input method.

I deal with real clients (read older people) every day and they can barely read the actual text on the screen, let alone text that is skewed and mangled in an attempt to foil machines.

I wish people stopped trying to solve the CAPTCHA problem with other CAPTCHAs.

This proof of concept, while pretty cool from a geek point of view, doesn't do anything to solve the problem in a better way.

Stuff like hidden fields, timestamp analysis, crowd-sourced classifiers (like Akismet), on the other hand, do.

i gave up trying to do creative spam filtering long ago. email address obfuscation, greylisting, etc. i put my domains behind postini (shame they got bought out by google) and never have to deal with spam anymore. my e-mail address is in plain sight in lots of places, and i only get false positives once in a rare while that i have to login to postini and forward to my inbox.

same thing with spam comments on my site. i didn't bother with captchas or other annoying requirements like openid. it submits everything through defensio (http://www.defensio.com/) on the backend and if it looks like spam, you just have to put in an email address to manually confirm the comment and re-train defensio. otherwise people can leave anonymous comments without any hassles. the amount of comments that need to get manually verified are very low, and i never see spam get through.

Why is it a shame that Postini got bought out by Google?

Seems like it would be quite a bit easier to solve than the current text-based capchas. You don't even need to do OCR.

Hell, in it's current form it's entirely client-side; hardly seems like it should even count as a CAPTCHA. $(form).attr("action", $("#mc-action").val()) and you're done.

Even with server-side validation, it's still trivial to break; it only requires tracking a line through an otherwise blank image.

This is fundamentally unusable as a CAPTCHA, and can't be made significantly better. The whole point of a CAPTCHA is to be difficult for computers and doable for humans, hence stuff like warped characters and image categorization. Tracking a line against a blank BG is not difficult for a computer.

Yes. Not only is this easier to break than a character captcha, it's more painful, fiddly for the user.

I don't like it for accessibility reasons, but if you have a site with n disabled users (say, a site for archers?) it might work well.

Certainly, not hard for spammers to break, but as long as it doesn't have widespread use, they won't bother putting in the effort.

> as it doesn't have widespread use, they won't bother putting in the effort

But this can be said about almost any Javascripty custom trick, and there are ones that no effort from user and don't have accessibility issues beyond requiring JS.

Naturally if you'd had a quick look at the readme/roadmap, you might have noticed that this is a proof of concept :o)

V1.0 will combine it with a standard PHP captcha, which is replaced onload.

I did look at the readme. The client-side issue isn't a real problem. The fact that it's easy for computers to solve, on the other hand...

I get that it's a proof of concept, but it's a concept that doesn't work. You can't make recognizing a line easy for humans and difficult for a computer. The best you could do is introduce noise and make the line a shape that humans are likely to recognize... and bam, we're back at warped characters.

It would be easy to solve if you were doing it perfectly... harder otherwise... and I bet if you do a perfect shape (ie completely on the line) it gets refused. Or at least, that would be clever if so.

It's only slightly harder to exaggerate the strokes some small but random amount.

this was already submitted & commented: http://news.ycombinator.com/item?id=2620870

One of the key notes of humane UI design is that the average user is terrible with the mouse. Joel Spolsky touches on this in one of his articles:

http://www.joelonsoftware.com/uibook/chapters/fog0000000063....

Depending on the sensitivity, this CAPTCHA could definitely drive away users.

Very interesting - thanks.

I'm looking to include a "Switch to default captcha" option for those concerned with usability (myself included)

If I write a completely stupid bot that just submits a rectangle, I'll have 10% chance of getting it right.

You need a lot more shapes… but there aren't many shape/size/position combinations that are easy for humans.

You need complicated images, as plain shape/background (and in general shapes on background that are separable on histogram) are easy to trace.

I'd suggest taking a look at the readme - it covers this and more!

I don't see where it addresses problem of generating large enough number of shapes that are hard enough to recognize with computer vision.

I'm afraid that nice gesture recognition algorithm is not enough to defend against bots programmed to recognize known solutions & replay (slightly randomized) predefined answers.

There's almost no chance that my elderly parents would have the dexterity to pass this.

Interesting idea. I thought it might be more confusing if it described the shape to draw and put the 'prototype' line of a different shape in the box. Robots would be trying to match the prototype, humans would be drawing the requested shape.

For whatever reason I don't have the dexterity to draw a correct shape very quickly :-) That suggests if the captcha was used a lot (like every time I submitted a comment or something) I would quickly become frustrated and stop participating.

It seems like this would be a total stopping point for mobile users, too.

It's kind of interesting that it uses the ribbon brush from mrdoob's harmony. I guess it would make a match more likely if you did it really quickly.

The plugin actually combines two libs, the Ribbon brush is used only for display (could be any brush if you switch out that class in the JS), meanwhile the points you draw are also tested against the Protractor gesture recognition algorithm.

The recognition seems so-so - I drew something that looked NOTHING like the image and it accepted it. Are you using chaincodes for recognition?

Spammers don't have to respect DISABLED attributes on forms. Client-side tests are not trustworthy.

And how the hell do you expect blind people to be able to submit the form?

I was expecting to see something completely unsolvable on a trackpad.

But I was proven wrong: http://i.imgur.com/QO8pY.png

This looks pretty sweet, I wonder how the shape matching works.

Wow, that's the exact opposite of what I ran into:

https://skitch.com/jameskilton/fdcir/motioncaptcha-demo

It's a good idea, just needs to be a little more on the lenient side for those of us who aren't artistically inclined.

Edit: Hmm if you go faster it has a fuzziness to it:

https://skitch.com/jameskilton/fdci7/motioncaptcha-demo

That's thanks to mrdoob's Harmony, specifically the Ribbon brush (http://mrdoob.com/projects/harmony/)

I got the circle and after 8 tries on a trackpad I was unable to get it

Yeah, I'm planning to have a switch to revert to default letter-based CAPTCHA for cases like this. thx.

Excellent work! reCAPTCHA is rather unfriendly to non-English users.

thanx :o) watch the repo to see when it becomes ready for use on live websites.

Here is another take on captchas, with the source.

http://jordan-adams.co.uk/humancheck/