# Impossible Captcha with non-keyboard characters

Am I a human? Yes. Can I type phi off the top of my head? No.

• That's Phi, not Theta. May 5, 2010 at 13:05
• This is probably a bug. Urrgh what the what? May 5, 2010 at 13:06
• @Kristo and all - thanks. Maybe that's why... 8-\ May 5, 2010 at 13:08
• Note that if you would have typed whatever you wanted instead, it probably would have worked as long as the first was "corrected". May 5, 2010 at 13:09
• How do we know that you're human unless you pass the CAPTCHA? Everyone be on your guard!! "Code Poet" is a human impersonator! He's trying to enlist your help to beat the CAPTCHA! May 5, 2010 at 13:15
• to add to Gnoupi's answer, SO uses re-captcha one of the words is known and one of the words is a scan from an old book. By giving the captcha to many people, they can accurately determine the scanned words the computer can't recognize. Effectively using small amounts of peoples time as powerful computer power to electronify books. May 5, 2010 at 13:18
• @Lumpy - if your comment had a checkmark next to it, it would be marked check. May 5, 2010 at 13:44
• As designed. A robot would not head off to meta, post this question, learn how to enter the CAPTCHA, then return to the page and complete the challenge. So clearly you are not a robot, and the CAPTCHA worked! May 5, 2010 at 15:07
• @Craig I don't know. That sounds exactly like a try - catch to me. try { ReadCaptcha(); } Catch(InvalidCharacterException ex) { PostToMeta();RetrieveAnswerFromFoolishHumans();} Finally { SpamDeluge(); } May 5, 2010 at 15:22
• Are we human? Or are we dancers? May 5, 2010 at 20:20
• I got this recently with a photon-symbol, and also one with chinese letters ><
– user146787
May 5, 2010 at 21:50
• Related: TODAYS REVISIONS WTF?! meta.stackoverflow.com/posts/48840/revisions
– user146787
May 5, 2010 at 21:56
• @Koning - i noticed that too. interesting.. May 5, 2010 at 22:30
• @Earlz: So...? They're just as bad as your titles. May 6, 2010 at 0:17
• You don't even need TeX. Just enter ϕᴍ,ᴘ(x) in plain text! Feb 7, 2013 at 12:35

Each new word that cannot be read correctly by OCR is given to a user in conjunction with another word for which the answer is already known. The user is then asked to read both words. If they solve the one for which the answer is known, the system assumes their answer is correct for the new one.

So therefore if nobody else figured out this one, you would be the first and you could legitimately type anything and succeed at it.

• So that would explain why it let me through when I accidentally mistyped a captcha... May 5, 2010 at 21:17
– user148312
May 19, 2014 at 19:21

Pfft... that's easy. Try this one:

• I smell a robot! May 5, 2010 at 14:10
• Burnt waffle reform. easy. May 5, 2010 at 14:40
• @Jon: I don't think that █ is an 'ARABIC PLACE OF SAJDAH' (U+06E9) May 5, 2010 at 14:53
• @Kenny: Ummm... they had an unfortunate fire? May 5, 2010 at 14:57
• Pretty easy on on iPhone >++++++++++[>+++++++++++>+++++++++++>++++++++++++><<<<-]>>+>----><<<<>.>.>.
– user146787
May 5, 2010 at 21:59
• Is it ▓ Reform? May 5, 2010 at 22:00
• It looks kind of like a cake. Maybe it's "torte" reform.
– user164291
Aug 8, 2012 at 20:53

As promised, here's the one I got a few days ago:

Edit: One more from just now (looks like they are scanning math books):

• ++ wtf indeed. . May 5, 2010 at 22:50

This is a trick question: you fail if you can type it.
The cat and mouse game continues...

Remember that, if the challenge is too "hard" to solve, you can request a new one with the "refresh" button.

• Klaatu ampliti ni*hack cough*!
– user164291
Aug 8, 2012 at 20:54

You misunderstood - you are supposed to solve the equation as well.
I know it's tough but we have to keep the cyborgs out of Meta.

Readable, just confusing. It seems like reCAPTCHA is now digitising house numbers on Street View as well ;)

• Nice. And odd that they know where to find the number, but then still need a human to confirm its value ;-) Mar 28, 2012 at 5:47
• I've seen this recently. No else that I know agreed with me, about those being house numbers though. I am so happy that there is some else who believes that they are house numbers too! Aug 8, 2012 at 20:24
• Seriously dafuq!! o.O Aug 16, 2012 at 9:34
• Are there 2 pi before number? Aug 23, 2013 at 9:07

Now, isn't at least one of these supposed to be a real word?

• Google: 'Your search - joutandt - did not match any documents'. lolz - what are the odds of 0 google hits on a single word consisting of ascii characters? Aug 18, 2010 at 19:39
• What's more impressive, we're discussing it on the Internet and it's still a Googlenope! (Also, I totally thought the second "word" was in Arabic at first.)
– Pops
Sep 17, 2010 at 18:27
• Clearly it's "joutandt OOMMG!!!" Mar 28, 2012 at 6:22
• No, "18 15 23 44" don't count as a word in my book, even if rotated by 90°.
– MvG
Oct 5, 2012 at 19:56
• @SkySanders Your comment is the top result, but nowadays there's also a Google Books results from something published in 1813... Aug 3, 2014 at 22:06
&phi;<sub>M,P</sub>(x)


φM,P(x)

(or use LaTeX \phi_{M,P}(x).)

• &phi; doesn't work though :) it's clearly the capital letter Phi: ɸ. I am not sure of the HTML code for that though. May 5, 2010 at 13:49
• @Joshua: The capital Greek Phi (&Phi;) is Φ (U+03A6), not ɸ which is the Cyrillic Ef (U+0444). There's also a phi symbol ϕ (U+03D5) which may render like the image, depending on the font. May 5, 2010 at 13:54
• @Joshua: &phi; and &Phi; -> φ and Φ May 5, 2010 at 14:23
• You know, providing LaTeX equations in captchas would be excellent for mathoverflow.com to keep out the riff-raff. They're always complaining that they get too many elementary-level questions there... ;) May 5, 2010 at 14:49

I actually got 4 Greeks in a row. Sharing my favorite for posterity:

First of all, I am human but no human being can decipher the ReCAPTCHA I just encountered.

• Someone skipped differential calculus.
– user156620
Apr 23, 2011 at 8:45
• You only need to type "helects" for that
– YOU
Apr 23, 2011 at 8:49
• @YOU: Oh, there's no need for capitalization? Apr 23, 2011 at 9:17
• @Hendrik, Yeah, I used to type like that, and It works, IIRC.
– YOU
Apr 23, 2011 at 9:25
• What's so hard about (\deltaa_i)/(\deltaa_(i-1))? Feb 25, 2012 at 16:51
• @TomWijsman: It's \partial a_i/\partial a_{i-1} also pronounced "del", "dou", and other weird stuff. math.stackexchange.com/questions/110565/… Mar 28, 2012 at 6:24
• I guess so, that's over the top of my head... Mar 28, 2012 at 6:30

This is the best (or worst) CAPTCHA I've recieved.

• Oh, that's \sum_(i=0)^n((-1)^n)/(2n-1^(\Delta^n))). Feb 25, 2012 at 16:50
• @TomWijsman: it's clearly (-1)^50 :)
– CSᵠ
Feb 27, 2013 at 21:20

I just got one with an integral from -∞ to ∞. Is reCAPTCHA digitizing math books this week?

• It's been for some time. I recall an integral from a few weeks ago. May 5, 2010 at 17:16
• Hmmm... I wonder if we're supposed to solve these? May 5, 2010 at 20:34
• @Bill: But there wasn't anything to integrate -- just the integral symbol. That's why it was so frustrating! May 5, 2010 at 21:40

I would have entered ompx.

You can also just press F5 to get another one.

– Pops
May 5, 2010 at 14:20
• Is that popular demand? Don't think so.
– user138231
May 5, 2010 at 14:24

I think it is the symbol of diameter. Well... I can: ∅ and ϕ

This are some details of phi:

UTF-8: 0xCF 0x95
UTF-16: 0x03D5

C-form (octal escaped UTF-8): \317\225
XML-form (decimal): &#981;


• Are you a human? May 5, 2010 at 13:08
• @code poet: Yes. In linux there is a very handy app that allows you to access all symbols. May 5, 2010 at 13:10
• NULL SET and PHI are not the same glyph. May 5, 2010 at 13:25
• @Quack Quixote: correct, the correct glyph is U+03D5 Greek Phi Symbol (referring to the posted image, it is the incorrect glyph). Windows also has a character lookup, called the Character Map. May 5, 2010 at 13:38
• Sadly, X's Alt Gr key mapping includes ø, but not phi. May 5, 2010 at 14:21
• @Mart: What app is that?
– John
Mar 5, 2011 at 2:17

Distorted text CAPTCHAs can be a little stressful also!

• When did SE turn into reddit ? Jun 2, 2015 at 16:00
• Must... Not... Type...
– user474678
Aug 23, 2019 at 19:11