Any ideas on how to prevent screenshots on Roll20 ?

Hello o/ My question is quite simple : would there be any simple trick to prevent players from taking screenshots of the Roll20's board ? I'm currently running a dungeon where there is some kind of glyph patterns to remember. Players see it for like 20 seconds and then have to rewrite it later based of their memories. Yet, I know my fellow PC and they might want to cheat on this part to avoid terrible fates occuring if they fail to resolve the riddle ... Any ideas about how to do this ? Or maybe another way to level-design this part of the dungeon ?

There's no way to do stop screenshots on a computer screen, without hijacking the players PCs (which is illegal).

Probably finding a different mechanic which relies less on memory and more on something like logic/problem solving. A riddle or some sort logical analysis. Hard to say what might be appropriate without knowing the specifics. You could push it down to a character check to see if they remember, rather than relying on the players.  All of that is really getting off into “not Roll20 specific” territory. Probably better discussed on reddit or similar. 

You might try talking to your players about not cheating, too.

There is a portion of Master's Vault that is similar, but not exact.