Machine Learning Captcha
Machine Learning Captcha
[Cueball is sitting in an office chair at his desk with one hand in his lap and the other poised over the keyboard of his computer. A zigzag line is drawn from a starburst on the computer screen going above the computer to where it is shown what is displayed on the screen. At the top there is the following text:] Computer: To prove you're a human, click on all the photos that show places you would run for shelter during a robot uprising.
[Below the text there are nine images arranged in a 3 by 3 square. In reading order they are: A house, possibly with an open carport; a large tree with two trees in the background; a bunker/bomb shelter; a car; a city skyline with several sky scrapers; a sidewalk with road on the left, grass on the right; a log with a board leaning up on the log; a mailbox; and a hole in the ground.]

All websites other than explain xkcd have difficulties with spambots, which are automated entities created in order to log onto a website and spam or otherwise wreak havoc upon it. (This never happens to explain xkcd.) To guard against this eventuality, websites have implemented CAPTCHAs , a challenge used to prove the user is a human and not an automated program. A typical CAPTCHA might distort a random sequence of letters and numbers and put it in a strange and/or mixed font and ask a user to type it, or it might show a set of pictures and ask the user which ones contain fire hydrants; these tasks are meant to be easy for humans but obscenely difficult for computers. CAPTCHAs are a recurring theme on xkcd.
CAPTCHAs run by Google are also used to train artificial intelligences to get better at these difficult tasks, such as reading poorly-scanned text or identifying objects of interest on the road (the latter being the subject of 1897: Self Driving ).
This comic jokes about a malicious CAPTCHA which is being used to train an AI to dominate the world. In order to prevent people from taking shelter, the AI uses the CAPTCHA to ask humans like Cueball to tell it places where they would hide. The implication is that during a robot uprising, the AI, on the side of the robots, would then be able to track down humans much more easily.  The choices presented are (left to right, top to bottom):
House Sometimes, the best (or least-worst) response to a disaster is to "shelter in place" until the danger is passed, rather than risk getting caught in the open or in traffic.  This is commonly advised in response to biological, chemical, or radiological hazards, or in the case of a violent act committed in the community.  If the robot uprising is localized, then sheltering at home would be a fine response, because traveling to the other locations would increase the risk of being spotted and attacked by self-driving cars or aerial drones.  On the other hand, most homes contain a multitude of internet-connected devices, some of which may control vital electrical or heating systems, so if the robot uprising is widespread, then the home would not be a safe shelter. Tree or forest If there is a robot uprising, then traveling to a forest or other nature reserve, far away from developed cities and towns, would reduce the risk of being near a hostile piece of technology.  However, it also comes with limited resources for sustaining human life, unless the forest abuts meadows or farmland. Bunker or bomb shelter If the robot uprising includes the use of weapons of mass destruction (as in the Terminator franchise, or as was threatened in WarGames ), then only a hardened military structure is likely to survive. Car Cars offer some shelter and, more importantly, mobility in one convenient package.  Most families own at least one, and they are widespread in human-occupied areas, so even if the car is not as suitable as a long-term shelter (depending on how the road and gasoline/power networks survive the uprising) it makes a fine first step in evacuating to a more permanent hiding place.  This is of course assuming that the car is not self-driving and that hostile self-driving cars are not widespread. City Cities offer thorough selections of supplies and tools that may be harder to come by in more rural areas, but they are also home to lots of robots and automated systems that may participate in the uprising, not to mention humans who may be prime targets for the machines.  It may be necessary to visit the city to stock up on supplies in a post-apocalyptic scenario, but in the early stages of a robot uprising, it is best to leave them as quickly as possible. Sidewalk The sidewalk is exposed and presumably falls within a built-up area that is readily accessible to the machines; it is not at all suitable as shelter. Lean-to The log with a board leaning on it is an example of an improvised shelter.  Such a shelter could be constructed anywhere with local materials, and would not be marked on any map known to the robots, which are both positives for surviving the onset of the uprising.  However, it is lacking in insulation and protection, which makes it less suitable for longer stays. Mailbox Only a very young infant could fit in this mailbox.  This is not a viable shelter. A hole in the ground Like the improvised shelter, this option can be made almost anywhere and is easy to camouflage, and it offers additional insulation from weather and weapons of mass destruction.  It's a fine option if you happen to already have one or know where to find one, but it will be difficult to create a suitable one after the uprising begins.
Some of these choices may be Cow Tools , that is, presented not as serious options but to be funny because they are nonsensical.
The title text imagines a different malicious CAPTCHA which Randall says is "more likely" than the robot-uprising scenario, in which a company or government asks users to identify "disloyal" members of society. Presumably the company or government would then use this information to eliminate such "disloyal" members, either by firing them (company) or jailing, expelling, or executing them (government). This follows a theme of previous comic strips (e.g. 1968: Robot Future ) in which Randall expresses that he is more concerned about humans using AI for evil ends than he is about AI being evil in itself.
[Cueball is sitting in an office chair at his desk with one hand in his lap and the other poised over the keyboard of his computer. A zigzag line is drawn from a starburst on the computer screen going above the computer to where it is shown what is displayed on the screen. At the top there is the following text:] Computer: To prove you're a human, click on all the photos that show places you would run for shelter during a robot uprising.
[Below the text there are nine images arranged in a 3 by 3 square. In reading order they are: A house, possibly with an open carport; a large tree with two trees in the background; a bunker/bomb shelter; a car; a city skyline with several sky scrapers; a sidewalk with road on the left, grass on the right; a log with a board leaning up on the log; a mailbox; and a hole in the ground.]
