Captcha
Explanation
The Joke
The comic shows a CAPTCHA test -- the familiar "Prove you are not a robot. Select all the stoplights" challenge that websites use to distinguish humans from bots. In the first panel, we see the grid of images from a street scene. In the second panel, someone selects squares that contain stoplights. In the third panel, the system declares "You have failed. Try again."
The final panel reveals the twist: the test-taker is a self-driving car (shown as a small autonomous vehicle), which says "Shit." The joke is that a self-driving car is, in fact, a robot -- and one whose entire job depends on being able to identify stoplights. It has failed the very test that its core functionality should make trivial, while also being correctly identified as a non-human by the CAPTCHA system.
The Humor
The comic works on multiple levels. First, there's the irony that a self-driving car -- a machine specifically designed to recognize traffic signals -- has failed a CAPTCHA about identifying stoplights. Second, CAPTCHAs are designed to keep robots out, and the self-driving car is literally a robot trying to use a human service. Third, there's a meta-joke about Google's reCAPTCHA system, which actually uses human responses to these image identification tasks to train its self-driving car AI (Waymo). So in reality, humans solving these CAPTCHAs are teaching self-driving cars to recognize stoplights -- the very thing the car in this comic has failed at.
References
CAPTCHA stands for "Completely Automated Public Turing test to tell Computers and Humans Apart." Google's reCAPTCHA v2, which uses image identification tasks like selecting stoplights, crosswalks, and bicycles, has been widely noted to be training data for Google's computer vision and autonomous vehicle projects. The comic plays on this well-known connection between CAPTCHA image labeling and self-driving car technology.