Captchas: Why We Need Them, How They’re Evolving, and How You Can Solve Them More Easily

As humans living in the modern world, we have to claim we’re not robots fairly often, and we’re not even living in some futuristic science-fiction dystopia. Regardless, whether you’re checking an “I am not a robot” box, teaching an AI what constitutes a “sign” (Hint: the “correct” answer is whatever the majority of other users have picked; try to think like the crowd), or solving math problems, the goal is always the same: stop bots from messing up websites, and maybe use the humans solving the captchas to digitize some books, train some image-recognition software, or generate some ad revenue. But there’s more to captchas than meets the eye, and they’re far from foolproof.

Why do we need captchas?

CAPTCHA stands for “Completely Automated Public Turing test to tell Computers and Humans Apart,” which, aside from being a truly elegant acronym, tells you most of what you need to know. The idea is, as Google’s reCAPTCHA motto goes, to create a task that is “Easy for people, hard for bots.”


“Bot” generally refers to any program that is set to automatically complete some process, whether it’s posting news on Twitter or leaving spam in website comment sections. Used correctly, these programs are fairly useful, but they can also be used to generate useless/ad-ridden/malicious content, overwhelm a site with signups, rig online poll results, scrape email addresses, or do any number of other unpleasant things. It’s just best not to let them in.

What exactly is a captcha?


If you’ve been around the Internet for a while, you’ll remember that for most of the 2000s, the most common captcha type was a strip of distorted text with some string of alphanumeric characters in it. This is no longer a very secure form of captcha, but when Google acquired reCAPTCHA in 2009, it was still good enough to get most bots. Since then, Google has switched to the more secure “I am not a robot” boxes (which actually monitor behavior like mouse movement and browser information to check if you’re a bot) and image-recognition challenges. Audio-based captchas are still around, though, and they are surprisingly easy to break with speech-recognition software.


The image-recognition captchas have had their own set of issues, as they can be a little ambiguous for human respondents. As mentioned above, though, there is no right answer – since the computer doesn’t know which pictures are storefronts and which are schnauzers – it just accepts the majority human opinion as correct. If 75/100 humans decide to label a blurry picture of a mop as a schnauzer, the computer will assume that the mop is a schnauzer and will mark you wrong if you don’t label it as such.

But there are plenty of other captcha options as well, and they can get pretty creative. These are just a few of the ideas that have made it onto various websites.

The slide-lock captcha:


The math problem captcha:


The drag-and-drop captcha:


The image orientation captcha:


The logic/grammar captcha:


There are also some captchas you never see, such as the honeypot captcha, which involves adding an invisible field to a webpage, waiting for a bot to fill it out (humans won’t, as they can’t see it), and subsequently kicking the bot off. Then there’s Google’s “invisible captcha,” often paired with their box, which watches how you browse around a webpage (mouse movements, scrolling, clicking, general behavior) to see if it should give you an image-recognition captcha as a double-check.

Captchas: making the world a better place

You may not know it, but the cumulative hours you’ve spent proving you’re not a robot may have actually made a difference. reCAPTCHA, now Google’s captcha service, was originally designed by Luis von Ahn (now better-known as the founder of Duolingo), as a way to use wasted brainpower to digitize books. By presenting users with a scanned word from a book or newspaper, this system could both confirm a user’s identity and take a sort of opinion poll on what the word was. If enough people agreed on the word, the digitization system would accept the answer into the ebook version.

After implementing this system, it only took two years to digitize the entire Google Books library and the entire New York Times archive. By 2012 they switched over to using humans to input house numbers pulled from Google Street View.


In 2014, things took an ironic turn towards the robotic: image-recognition captchas. These work on the principle that machines aren’t very good at figuring out what’s in a picture, but, as described above, they’ve been pretty effective at training AIs to do just that. Since this captcha will eventually work itself out of a job, it is being phased out in favor of the less-visible behavioral/tracking-oriented ones.

In conclusion: am I a robot?

As artificial intelligence, deep learning, and a host of other advancements come down the pipe in the next few decades, captchas are going to have to evolve as well. Most captchas in existence have already been cracked, and it’s only getting easier. Training a machine to read distorted-text captchas now takes about fifteen minutes. Perhaps the only thing left in the future will be biometric captchas (hope you like facial recognition scans!), or perhaps we’ll wake up and discover that the singularity has already been reached, and we were the bots the whole time.

Image credit: Chippee via bad google recaptcha house numbers

Andrew Braun Andrew Braun

Andrew Braun is a lifelong tech enthusiast with a wide range of interests, including travel, economics, math, data analysis, fitness, and more. He is an advocate of cryptocurrencies and other decentralized technologies, and hopes to see new generations of innovation continue to outdo each other.


  1. I guess I must be a robot. Since image-recognition captchas debuted, I have not yet been able to successfully solve even one. :-) AFAIAC, no big deal. If they do not want to let me in, it’s their loss, not mine. There dozens of other similar sites that do not guard their virtue so tightly. I am not going to play wack-a-mole for half an hour to get into some site of dubious value.

    1. Yeah, image-recognition captchas are way out–at first they were hard for robots and hard for humans, now they’re easy for robots and still hard for humans. If you see a site using one, it may be a sign that they don’t keep up with security trends and haven’t yet had a big enough bot problem to provoke them into updating.

  2. I find some challenging as I have a cataract in one eye an artificial lens in the other. The visual CAPCHA are hard for the visual impaired as I have found out. Since they are not covered in the American’s with Disabilities ACT, I still would like to “see them better “, or use a different method. This article had some I have never experience before that would be easier for f=me with vision problems.

    1. If you browse the internet without privacy extensions or a VPN, odds are you’ll run into captchas less and less over the next few years, so you’re in luck! Most captchas now are invisible, using your behavior to check for your robotic qualities, and they’ll probably be more widespread quite soon.

  3. Don’t be fooled by this shill.

    Recaptcha by Google isn’t ONLY being used to identify bots but ALSO to identify individuals across the entire web.

    Recaptcha is AI deep learning and there’s no excuse to include it every where including in SINGLE PLAYER video games like Max Payne 3.

  4. “…the singularity has already been reached, and we were the bots the whole time.”
    I can prove that the above is true and Google has been obsessed with TRACKING me MANUALLY and algorithmicly for 3 years. They are obsessed with knowing everything I know at all times and they force the worlds biggest youtubers to make “fake news videos” based on my findings and my attempts to make those findings public. They have Roberto Blake posing as a friend to me but he’s actually a spy. They do a lot more than that. The spam dislikes update is because of me. The removal of the geo data from the new studio beta is because of me. …and so much more. pls subscribe but message me for more info about this topic I do not make videos about it anymore due to the negative impact they have on the world… because of the advantage they give to our slave owners…. Google (or whoever controls it all)

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