I doubt I'm the first to discuss the issue of the increasing number of bots running around the world. I doubly doubt I'm the first to recommend a solution.
I have an idea that could limit the possibility of bots and I haven't seen anyone else post anything similar, though I do not claim to have read everything ever written about ESO. Simply, bots "teleport" around to various possible nodes harvesting if they exist. I've noticed I've never seen them go after chests. The reason behind this is likely the mini-game required to unlock said chests. Introducing a mini-game to harvesting shouldn't require much additional code or interface in the game (admittedly, I've never gotten a look at the code behind ESO, so I am willing to be wrong here).
As it stands, the avatar runs to a node, presses E (default) to interact with the node and the user waits the appropriate 2-3 seconds for the avatar to "collect" the resources. My proposition is to introduce a "mini-game" where instead of waiting 2-3 seconds the user must do something. This can be anything from pressing 1-3 correct keys within a timed window, pressing a key/mouse button for a period of time and releasing when visually cued, really anything that requires a visual element that bots are bad at replicating.
Additionally for gameplay/immersion, nodes can be coded to be difficult; just as chests range from simple to impossible, nodes can range from rich to decayed and subsequently be easier or more difficult to harvest.
As I've said, I don't believe the coding would be difficult or complicated as most of what I have proposed is already in the game in other forms (mostly the chest mini-game). I'm curious what others think about this suggestion. If it has already been suggested somewhere that I missed, I'd love to see a link so I can give a thumbs up in the appropriate area.
TL;DR Version: Introduce a visual mini-game to node harvesting where bots will have a hard time replicating human interaction. Replace the 2-3 second waiting period for the user with said mini-game.