This explains the picture very well, and I think this is the correct answer. But if you click on the reddit link above, the comment has the line is upvoted more than 10. The asker also understand the meaning of it too. Can you explain that? – Ooker – 2016-10-31T10:56:10.310

1why do you remove the image? I guess it makes the answer easier to understand and more attractive? – Ooker – 2016-10-31T10:58:05.033

4@Ooker: The Reddit comment is not particularly funny or remarkable in itself. The point of it is simply to remind the other participants in the discussion that "esker" is the name of a particular landform in geology. It's not all that common a word, but the hint is enough to convey to the readers that it's a real word and they should try looking it up. Some readers found that nudge helpful enough to upvote it. – hmakholm left over Monica – 2016-10-31T11:01:16.727

11@Ooker: Escher's estate maintains copyright on his works, and the general Stack Exchange policy is not to embed infringing images in posts. – hmakholm left over Monica – 2016-10-31T11:02:51.763

1

This image is from Wikipedia https://en.wikipedia.org/wiki/Drawing_Hands#/media/File:DrawingHands.jpg it says "fair use"

5Just because some Wikipedia editor somewhere decided, for his own unknowable reasons, that embedding the image would be fair use doesn't necessarily make it so -- and in particular I'm not prepared to import that judgment to my answer here. – hmakholm left over Monica – 2016-10-31T11:08:50.057

2In fact the Reddit comment is a direct quote from the article itself (which itself quotes it from Munroe's book), and therefore points to the part in the article where the explanation behind the cartoon is found. – hmakholm left over Monica – 2016-10-31T11:15:25.063

Thanks, I focused too much on the "outside my home" bit. As for the image, taking an image for education purpose is a fair use, and won't infringe the copyright. But I'm pretty sure that you know this as well. So why don't you consider this? And what is the "import that judgement"? The judgement of fair use? – Ooker – 2016-10-31T11:16:01.400

12@Ooker: Using an image for education use is fair use, when the image is the subject itself. It would be hard to teach about the works of M.C. Escher without actually showing a sample of them. It is not a general escape clause. In particular, diagrams in school books made for those schoolbooks are very intentionally for educational use, and yet you can't copy them into your own school books. – MSalters – 2016-10-31T12:21:22.507

@MSalters sure, but as far as I can recall, a copy will be considered as a fair use if (1) use for research or education purpose, (2) doesn't make any harm to the original author, and (3) the copied material isn't a large proportion that build up the product. I think using the drawings here satisfies all these three conditions. – Ooker – 2016-11-01T09:04:30.673

@Ooker Fair Use isn't available under Dutch law. (Though we do have the right to quote.) – nl-x – 2016-11-01T12:49:41.887

@Ooker The copied material is 100% of the product. – Marquis of Lorne – 2016-11-01T21:19:45.430

2@Ooker: You might have the fair use right to use someone else's work, but you still don't have the copyright, so you can't license it under Creative Commons, and you can't post material to Stack Exchange unless it is CC BY-SA licensed. – Ben Voigt – 2016-11-01T22:37:59.670

@BenVoigt I understand now. Is it not a problem of fair use or not, it's about the contradiction of licenses. Because the works of Escher are copyrighted, then using them under the CC license is illegal, is that correct? – Ooker – 2016-11-02T12:04:05.910

1@ooker Giving someone a license to copy it under the terms of CC BYSA is illegal. Only the copyright holder or their agent can issue new licenses. – Ben Voigt – 2016-11-02T14:50:57.113