Bots use Pixel colors and some use pic files to ID objects in game.Any botter needs static images and colors to create an efficiant bot.Without static images and colors theres nothing to script.
The ingame botters use the minimap as there static image...there icon is blue...the other players are white...So u make a script that sees your blue spot on the map as a reference point...you then calculate the direction and distance to the white circle with alittle math and that will let you know where to click to move in the direction to the player your following.
They just constantly do this while you kill everything.If they idle for a few seconds not moving the script says to teleport back to town and use another flag...this is there error defence basically.
The point is since static images and static colors on the minimap are what there using... make the minimap dynamic or remove it all together.The bots will have no static reference point and will have no way to identify anything.
No different than anything players make bots for...same as the ah...make things more dynamic and it will be much harder if not impossible to script
As for AH bots they can do what they use to block password spammers...when u want to buy an item you have to enter a picture based code with numbers and letters first