Not sure it's so hard, first you introduce some randomness and inefficiencies in the gathering process so that it's more credible that it's a fallible human that's doing it.
And as a second crucial step, you hook groups of bots into a "monitoring computer", at which an actual human sits and responds "No, I'm not a bot lol." when the supposedly fatal question arrives from an admin. You can even outsource this to the third world.
You've never played WoW, have you? "Randomness" is a dead giveaway of a bot. Other players will grief you, report you, and you will be banned quickly.
Just the computer vision aspect of it alone would be amazingly hard.
Efficient goldfarming (e.g., with a frost mage that can take on 15-30 monsters at once) involves carefully coordinating a complicated series of actions where timing is critical and reacting quickly and intelligently when things go wrong is the difference between living and dying. It involves making complicated judgments about relative positioning, reasoning about surroundings, cause and effect, and other things that require human-level intelligence.
If you can make a bot that can seek out and kill monsters in a non-trivial manner without dying all the time there's no reason you couldn't program a robot to replace a wide variety of menial real-world jobs. The consequences would be tremendous and using it to make $20/day off the Internet would be retarded because you could license the technology for billions.
Bots don't require computer vision or any kind of sensory input; they can extract the native data they need straight out of the application's memory space. Effectively gaming bots have "perfect information". So the bots actually have more timely and accurate information than humans do, they can react quicker than humans do, and they can react as intelligently as your programming skill allows.
Check out http://www.easyuo.com. That application allows you to easily automate Ultima Online. Whilst deciphering WoW's application memory would probably be harder, an equivalent program is certainly possible (it probably already partially exists in various forms), and intelligent bots are a simple step after that.
Unfortunately, once the memory accessing has been abstracted away, programming a competent WoW bot is not a difficult task. The WoW bot doesn't have to be as awesome as the best human players, nor need it be ultra-efficient. What it lacks in ability it makes up in working without fatigue indefinitely.
Bots don't require computer vision or any kind of sensory input; they can extract the native data they need straight out of the application's memory space.
I'm pretty sure WoW keeps track of all applications running on your computer. I think the way people do it is by using a hub and packet sniffers on a separate computer, although I imagine WoW traffic could easily be encrypted... so shrug.
All this hypothetical talk is very nice, but there actually is a wowbot that Blizzard has been unable to effectively use countermeasures against, called MMOGlider. They've decided to simply sue after repeated failure to solve it technically.
And if randomness is a dead giveaway of a bot, then don't implement it?... I was suggesting to add it but if it actually ampers your goals then make a fully deterministic bot...
The point of bots is that they don't have to be efficient, just marginally effective and able to run with limited or no supervision. The solution to inefficient bots is easy: create more instances.
but therein lies the rub: it's easy for the administrators of the game to realize that no real person in the right mind would sit in the same location for 3 days and go after the same creatures over and over.
Make the bot change locations and target creatures from time to time?... The point is that whatever heuristics are discovered to pinpoint bots won't be effective very long because of arms-race dynamics.
And as a second crucial step, you hook groups of bots into a "monitoring computer", at which an actual human sits and responds "No, I'm not a bot lol." when the supposedly fatal question arrives from an admin. You can even outsource this to the third world.