> Ever see those black boxes over censored documents? It's obviously better than blurring, the only information you get is the size of the box.

Actually, quite a few times in the past with that method, you've gotten the complete text, because someone uses a format that includes the text as text (like PDF) and then dropped a solid-black box over the text, which looks like the text is obliterated, but preserves the entire content in the file.

One time in college. A teacher did something like this with hw and solutions being "hidden"/"censored". And I was easily able to get around it and have all the solutions :/

One of our lecturers did something similar, but with class grades. They started from a complete list of grades in Excel, and for each student, deleted all grades but that student's grades and then saved a copy.

Unfortunately, they did this without disabling the Excel feature that saved undo data in the file, so anyone in the class was able to hit Ctrl+Z a couple of times and see the entire list of grades.

Which, depending on the font, can be enough to reverse-enginner the text, particularly if there is a smallish list of options.

Of course, if you block out a whole line, then things get much, much harder, basically impossible. There are many possible lines!