Good afternoon gentlemen (and ladies),
I come from other parts of the internet, and exposing shills, bots, socks, the technology they use and who uses them was a thing I used to do, and I will share my discoveries:
1) Image based captcha don't actually work on modern tech as most bot accounts have smart OCR systems that can detect even 'pretty bad' images and answer the captcha - the one you use for this board wouldn't even stop them (as you've discovered)
2) Text based questions can be answered by one of two systems:
2a) The operator 'adds the answer', or
2b) An AI inference engine tries to 'guess' or 'interpret' the question (EG What is 2 + 2? 4, for example)
3) You can thwart most bots by having a question/answer that changes on a daily basis (with no reuse) on top of a captcha, this can impede users however.
4) Bot operators are called 'handlers', and they can operate between 2 to 100 accounts. The average is between 15 to 30.
5) The software they use is commercially developed, although it appears some are homebrewed applications that run in Python (possibly to pair up with TensorFlow?)
6) Building a forum bot is incredibly easy: Python with mechanize library and BeautifulSoup (you might want to consider fighting fire with fire).
7) Governments, Corporations and Political groups all use bots. A prime example of corporations is the Net Neutrality spam. They use it to astroturf grassroots movements and artificially incite aggression/action/results (think Arab Spring).
8) Organisations confirmed: IDF (both professional and hired students), Mossad, CIA, NSA (Edward Snowden admits as such), parts of MI5, US Airforce, The MoD (specifically: the Army), MI6 (minor role), FBI (usually to honeypot/entrap/snare), GCHQ, FSB and whatever the KGB's replacement is. Democrats are more active with social engineering/bots/socks, Republicans are playing catch up. British politicians have yet to catch on, it seems. Pretty much every corporation does it - usually they send in their employees to write positive blurbs or counter-criticism (look at any critical article about Microsoft, Red Hat, systemd etc).
9) It costs a lot of money, but gets cheaper with automation and AI.
10) Handlers can't be in more than two places at once (mentally speaking: the bots log/alert the replies), and the more people simultaneously engaging them from different places (as their 'differing' accounts), the better as it overwhelms their responses and often they make mistakes.
11) Their bots are often 'tuned' to specific keywords and are capable of bulk-scanning threads (usually the last page to check for responses). If you mess up the keywords and don't mention them directly, the alert system appears to fail - they will get notified by other bot handlers however if it's something they've missed, and the new keyword will be added.
12) Some bot/sock accounts talk amongst themselves. Usually so one sets up, the other introduces information.
13) They will strawman arguments - present a weak front under one account, attack it with another. Don't accept or try to defend weak arguments.
14) The different groups have different agendas, from what I can see:
IDF: Solely concerned with topics that directly relate to israel, berating palestine (treating palestinians as non-human etc), attacking iran, tackling anti-semitism
US agencies: Whatever the current US politics are, always pro-military
UK agencies: Whatever the current UK politics are, always pro-British, sometimes pro-US (they have minor disagreements)
Russia: Usually anti-agency/anti-US/UK establishment, will bring up topics that advantage them (Syria, Palestine, US abuses of power)
Corporations: Anything directly relating to them (usually they target criticism)
Political groups: Shilling in favour of their political agenda/who they want you to vote for/attacking other parties.
I hope my observations are of some use. If I think of more I'll get back.