L2J Server

Still there must be both protection (server and client) like LG....

To be honest, a forced captcha on login(and some sort of command that needs to be inputed ) would do the trick in most cases.
I'll try to work something out and report here.

Or, just make more interesting servers without action repetitions and boring gameplay. The source of all the bots is bad game design. If a game is botable, that game is probably not interesting or sophisticated. ( Which is true for all lowrates ).

Besides that, there have been some papers on bot detection with data mining techniques but they are both performance killers and their false positive ratio is way too high to be used in a real environment other than the Academic garbage yard.

As for captcha systems, those new bigfoots, i mean ... players, have way more chances to fail the image than a bot does ...