p-bot
Explanation
The Joke
An elderly, bespectacled man who looks like a philosopher is browsing the internet and encounters a CAPTCHA prompt: "Are you a robot?" with a text box that says "Type answer here." Instead of simply clicking a checkbox or identifying traffic lights, the philosopher types: "The distinction is not a meaningful one." This philosophical non-answer -- which refuses to accept the premise of the question -- apparently serves as the correct password, because the next panel shows him welcomed to "the secret Philosophers' Internet." A note at the bottom of the page reads: "Any issues with the website are due to the fundamental limits of language."
The comic imagines that there is a hidden internet accessible only to philosophers, and the CAPTCHA to get in is not a test of whether you are human, but a test of whether you think like a philosopher. Only someone steeped in philosophy of mind would respond to "Are you a robot?" by questioning the validity of the human/machine distinction itself.
The Humor
The joke operates on the idea that philosophers are constitutionally incapable of giving a straight yes-or-no answer to any question, even one as simple as "Are you a robot?" The response "The distinction is not a meaningful one" is a perfect parody of philosophical hedging -- it sounds profound while being completely unhelpful in practical terms. The disclaimer about "fundamental limits of language" is a bonus joke, suggesting that even the Philosophers' Internet is plagued by technical issues, but the philosophers blame Wittgenstein rather than their server infrastructure.
References
The comic alludes to several areas of philosophy: the philosophy of mind (particularly debates about consciousness and whether machines can truly think), Wittgenstein's later work on the limits of language, and the general philosophical tradition of questioning the premises of seemingly simple questions. The CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is itself named after Alan Turing, whose famous Turing Test asked whether machines could be distinguished from humans -- making a philosopher's refusal to accept the distinction particularly fitting.