macros. Anything that you can automate in a game can be performed on the user's end via automation - in theory.
The reason for this is simple - game providers charge a fee to use their systems. They built the game & they want to be the ones to make money from it. People who can automate playing the game can 'farm' for the rewards handed out from playing. Sometimes this is called 'gold farming'. It can be for anything that is freely exchangeable between multiple players in a mutually shared on-line game world. Often the objective is to exchange those wonderfully coveted prizes for actual real-world currency.
This is behavior is not limited to games. Using automated scripts/macros/bot-programs to access web pages & follow links is a business unto itself. This is because online advertising works on two tiers - click-throughs and conversions. Just clicking on an ad makes somebody a fraction of a cent. Actually buying something after clicking through gets a lot more. The difference between those two prices is actually because of people using scripts. Since you can write a script to click on an ad link all day - it devalues that ad.
The captcha is one development in this arms race. However, there is commercial software that can defeat this with OCR out there. So if you can do this often and effectively enough to pay for your computers, an internet connection & some fancy specialized software and still clear a profit on top of it - then this might be for you.
Randomization seems to lie at the heart of every method to trying to subvert any automated script.
World of Warcraft does this kind of thing with activities like fishing - where it requires human interaction to respond to the random location on the screen and timing when your little float bobs so that you have to click on it. That way you can't walk away & let your computer fish all day. You could do it yourself - but you would have to sit there getting bleary-eyed, pale & fat doing so all day. Odds are that you can't support yourself and your family on selling virtual fish without a little help.
Kingdom of Loathing being wholly web-based is far more susceptible to this sort of thing and deals with it by randomizing combat results. Other popular web-based games do something similar.