Indeed. And famously, using black boxes as a background on individual words in a non-monospaced font is also susceptible to a dictionary attack on an image of the widths of the black boxes.
And even taking sharpie and drawing a black box doesn't mean the words can be seen at a certain angle or by removing the sharpie ink but not the printed ink.
Really, if you need to censor something create a duplicate without the originals. Preferably literally without the originals as the size of the black box is also an information leak.
