PoW

Why is it loading so long?

Your browser is calculating something to prevent abuse. The time it takes depends on the power of your CPU and, believe it or not, luck. Sometimes it takes like 5 seconds, sometimes 30 secs, so please be patient. If you want to know what's going on, go to the technical part.

Technical Part

The technique used, is called PoW, or Proof of Work. It is a way to "pay" for something by using your CPU. It's mainly used in crypto-stuff, but not in ClassQuiz. It's just used to prevent spam. Imagine it like a small fee you have to pay to upload an image, but you don't pay with money, instead by using your CPU intensively. The Proof of Work-algorythm used is called HashCash and is also used by Bitcoin. All in all, it's really simple (if you know what hashes are). Let me explain:
You're hashing a string with a counter until the first x characters (in this case 4) are "0"/zeros. That's it. Then, you send the counter to the server, who hashes it once, checks if the first x characters are really "0" and that's it.