Animated GIF captcha

April 12, 2009, 8:03 pm
Posted by Palmer in Projects

Man, captchas suck.

I think we all agree that captchas are fairly useless and more often than not cause more annoyance than good.
Most captchas are easily broken if someone sets their mind to it. Especially the one that came with this blog script! And even if they do stop bots they also stop blind or visually impaired people from using your system too.

But they are an unfortunate necessity, especially on the high traffic parts of my site like the mini polls where there's currently a captcha I hand coded especially for the mini polls. And so far I'm shocked to say I've not had any spam on there except the usual human spam.
However, today I have constructed an uber-captcha, which I quite like. It is slightly hard to read though.

This new one uses just PHP, no separate app (not possible on this server) or anything like that, and it generates an animated GIF file where every frame is totally unreadable, but when animated together it becomes readable to the human eye.
That's the idea anyway. I might have gone a bit overboard with methods to try and stop people using image filters on layers to get readable text again and it's now fairly hard to read: (hit esc in Firefox to stop it looping and see how messed up a single frame is)

New captcha

Anyway, feedback would be great on this. Any ideas on what I could do to make it more readable, yet still being awkward to crack.
Also, anyone who cracks it with their own code (no script kiddies) wins a free sandwich :D Fancy code or code in an esoteric language gets you a coke to go with your sandwich!

To play around with it and see what percentage of them you get right go to http://sandbox.palmnet.me.uk/gifcaptcha/, let me know what scores you get in the comments.

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Comments

Posted by   www
on May 6, 2009, 6:23 pm
Wow great job on this insane captcha. I got here from a google search for "Animated gif captcha" because I had the same idea of making one. I was thinking that the faster it looped, the easier the captcha would be to read with human eyes, but it wouldn't make it easier for bots. Can you increase the animated speed? (i.e. 1 ms per frame)
This way it would look like you see the whole word but it would be flickering.

Reply to this comment
Posted by Palmer  
on May 7, 2009, 5:44 pm
I did experiment with various speeds and the current speed seems fast enough to be readable and not so fast that it kills certain browsers, though in IE it is incredibly slow! But still just about readable.

It's not an optimal solution, but I thought it was a fairly novel one that hasn't been seen before to my knowledge and would be very hard to crack.

Reply to this comment
Posted by Boaz   www
on March 10, 2011, 10:50 am
Hi,

We make nice animated GIF CAPTCHAs - see in www.captchanim.com

Thanks!
Boaz

Reply to this comment
Posted by   www
on February 27, 2012, 10:19 am
You have written about lots of points in this article. There are actually magnificent, and I totally know what you mean.

Reply to this comment
Posted by   www
on May 13, 2009, 3:48 pm
A common type of CAPTCHA requires that the user type the letters of a distorted image, sometimes with the addition of an obscured sequence of letters or digits that appears on the screen but it was fairely novel.

Reply to this comment
Posted by Palmer  
on May 13, 2009, 10:14 pm
Grrr, spam >.<

Reply to this comment
Posted by Kairu   www
on May 24, 2009, 3:25 am
Looks like it would get the job done. I can see issues with slow running computers or browsers that don't swich frames fast enough, but other then that it seems quite nice!

I do agree with the above comment though. If you could find a way to loop it through so fast that it barely even flickers, it would still be hard to crack, but efficient for users to read. After that, you could take a regular captcha and just animate it to keep it from being read from screen properly. You could even randomize the frame order.

I might be trying too hard though....

Reply to this comment
Posted by  
on May 2, 2010, 10:30 pm
Hi.

Would you be willing to share the code for your captcha with the world (or at least with me)?

I would like to experiment with that to make it more readable.

I engineered the animated captchas for linksave.in (example: http://linksave.in/3755537704bddfc4776be0 ) and was on the lookout for ideas for an even better captcha, because they have been broken by jDownloader.org a while ago.

Best regards,
Kay

Reply to this comment
Posted by   www
on December 2, 2011, 8:10 am
WOW! Ideas like it I have never see in internet! Well done!

Reply to this comment
Posted by   www
on December 28, 2011, 4:11 am
..I am very happy to read this article..thanks for giving us this useful information. Fantastic walk-through. I appreciate this post.

Reply to this comment
Posted by   www
on January 11, 2012, 12:18 am
Well, yes, it will be impossible for bots to recognize it.

Reply to this comment
Posted by   www
on February 9, 2012, 2:12 pm
This article is great, however you should concentrate better on this theme. In general you did a good job.

Reply to this comment
Posted by   www
on February 20, 2012, 11:48 pm
I was searching for the guide how to so such captcha! Thanks for it a lot

Reply to this comment
Posted by   www
on March 5, 2012, 3:19 pm
You have done a cool article; I love how you illustrate this topic here. Thank you a lot

Reply to this comment
Posted by  
on March 12, 2012, 3:11 pm
nice, can you send me the code please ? its much more efficient then the current one in add comments form

Reply to this comment
Posted by   www
on March 26, 2012, 1:35 pm
Thanks for the nice ideas. Little doubt, you have done an amazing job because you are writing about this topic very well

Reply to this comment
Posted by   www
on April 11, 2012, 5:06 pm
Haha.. yeah, everyone us had those tough times with captcha

Reply to this comment
Posted by   www
on May 10, 2012, 7:18 am
I just want to say I’m beginner to blogging and truly savored your web-site. Most likely I’m likely to bookmark your blog post . You really have really good stories. Thanks a bunch for sharing with us your blog.

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