Not a terrible idea. I played on a EQ server that had a sort of custom captcha thing to prevent botting. It utilized the server's GM system to send a line of text in a random color, and asked what color the text was. You had 1 minute to use a GM command (@) to just type "#fishing color". If you didn't it sent you to homepoint. If this happened 3 times in 30 days, you got jailed.

I'm sure something similar could be done here with the @ GM system that wouldn't be difficult. Assuming botting is that big of an issue anyway.

You might be surprised by how much a bot can do. In this era, some bots did the following (this is not hypothetical):

(1) walk to a zoneline and back again,
(2) synth items for you when you have sufficient materials,
(3) walk to a vendor, sell items, and walk back,
(4) throw away trash, and
(5) send you a text message if someone interacted with you, mentioned your name, or you got a GM popup.

Of course, a bot couldn't get past a captcha. That thankfully still requires a person.

It is so easy to make potent bots that can literally do anything a player can do (in retail or in any server that doesn't protect from injection and memory alteration).

As long as dll injection, or read/write to/from memory is possible. There is FFACE, library made by RZN (the main guy behind Ashita Windower), that makes bot programming much easier as it allows the programmer to observe the game and act on it through an interface.

Here, Nasomi is putting a lot of efforts in detecting injection and external memory access. He also bans not only if packets are malformed, but if they don't comply with all the dummy packets that might be sent by the client after doing an action. Which leaves only bots that acts through image analysis, those are almost impossible to detect, but they are also much less flexible. It's possible to do the fishing game with it, but it's impossible for it to path in an environment. There's big chances that the dry zone update will be very hard to overcome.

The problem with Captcha as form of text is that it's sent from the server to the client, as readable data. It can be read directly from memory. It can also be read with OCR, such as Abby FineReader or google vision. It needs to be kinda... sophisticated, in an image, not in the FFXI chat log