The truth of the whole thing is that Google primarily relies on _behavior_ to detect bots. Captures are just an added layer of defense and serve as a pretty good way of seeding the behavior database. If some user appears to be a bot, serve them a captcha. If they fail, then that behavior was bot-like. Google is using captchas as a way to learn image recognition as well as bot behavior patterns. They know full well that they won't be able to rely on captchas for ever, but they will sure as hell collect as much data out of them as possible.
Actually I'm really tired of that Google's attempts. The other day I tried to find a something like a .txt file containing all the verbs. I tired searching for "finding resting searching" without quotes, Google kept giving me "find rest search", so I tried quoting it: " "finding" "resting" "searching" ", and adding more and more. Most of those were in anchors, not in text, I added: "allintext:"finding" ..." and here it is: "Looks like you are a bot! I can't allow you search for that." :)
Sometimes it's really tempting to write "Google" into Google. :)
Dear God, what's wrong with a query like 'allintext:"finding"' ?
I got curious and tried just this query, and sure enough Google said that the query looks like an automated one.
It means it's not the pattern of the queries that you have sent that triggered this 'you are a bot' response from Google. It's just the one query allintext:"finding". Removing quotes allowed it to be processed.
I thought it might have to do with the fact that a single word is enclosed in quotes; i.e., when a person is searching generally there is no reason why one would put a single word in quotes. On the other hand an automated search might enclose search text in quotes by default without parsing the text and figuring out whether it contains multiple words or a single word. But it turns out that is not the reason. A query like allintext:"Google sucks" still elicits the 'you are a bot response'. It looks like they ban all queries that enclose text in quotes for an allintext. Might be a bug.
Actually when a single word is quoted in a google search it does something - it turns off the matching of words against similar words.
For example if you search for the misspelled [netflixs] you will still get netflix.com, but you can turn that off by quoting the word with the query ["netflixs"]. The plus sign works similarly.
