These things are getting out of hand!
Igot thisa month ago and I still laugh thinking about it.
Anyway, I couldn’t figure out how to type it so I must be some sort of robot. 
Awesome username post combo! (Your name could itself be a captcha.)
If I understand correctly, the way Captchas work is that they have one word that is known (sometimes an actual word, and sometimes a string of “sensible nonsense” like the one in your image), and one word that is unknown. Typing in the first word confirms your human and/or Turing machine status, while typing in the second only helps them digitize the old books that provide the source text - if the first is correct, then they assume the second is also correct.
I’ve gotten something similar before, where I had a normal text string followed by something untypable (in my case, it looked like Cyrillic). I typed the first string correctly, then, lacking an Eastern European keyboard, followed it with a bunch of random text, and it passed. But right now, someone in Russia is reading a digital book and wondering “vat in ze hell does ‘grndsdf9ds’ mean?”
You’re talking about recaptcha which is a particular captcha group that is using them to pull double duty. A regular captcha is just a random arrangement of letters that a spam program shouldn’t be able to figure out. Recaptcha adds a word pulled from a digitized text using OCR. It doesn’t decide what the word means based on one person’s guess but takes them all in aggregate. If over a thousand captchas 97% say the word is homes then the program decides it most likely means homes. If the highest any particular letter order can rank is, say 4% because no one can read it and they just type random letters, then it assumes the words is unreadable and flags it for more careful and human based attention.
Δτₒ≃
Best I could do. Unicode doesn’t seem to support a subscript capital D. For reference, I typed each character by holding ctrl-shift, pressing “U”, releasing “U”, then entering the four-digit Unicode value for the character. (This was on my Ubuntu machine. I don’t know offhand how you enter Unicode on Windows.)
\Delta au_D \simeq
Here’s one I got a few months ago.
You were ordering porn, weren’t you? 
Dude it says **ofource ** :rolleyes:
I consider myself honored to be part of a group of people who, among other things, save screenshots of captchas.
Sadly, all mine are boring.
The strangest one I’ve seen is “republican messiah”.
Here’s one from Sarah Silverman that she put on on Facebook or Twitter a while back.