There was a programming competition, can't remember which, similar to IOCCC but more about problematic software? where the redaction was reversible despite being pure black, due to the format chosen allowing for left over information in the image (vastly reduced quality but it was enough to allow text to be recovered!) [edit: see replies!]
There was also the Android (and iOS?) truncation issue where parts of the original image were preserved if the edited image took up less space. [edit: also see replies!]
Knowing some formats have such flaws (and I'm too lazy to learn which), I think the best option I think is to replace step 6 with "screenshot the redacted image", so in effect its a completely new image based on what the redacted image looks like, not on any potential intricacies of the format et al.
Maybe you're referring to "aCropalypse". Also there was an issue once where sections with overpainted solid black color still retained the information in the alpha channel.
I also recall at one point some image file format that ended up leaking sensitive info, because it had a embedded preview or compressed image, and the editing program failed to regenerate the preview after a censor attempt.
Was a loooong time ago, so I don’t remember the details.
AT&T leaked information, as did the US Attorney's Office, when they released PDFs with redacted information. To redact, they changed the background of the text to match the color of the text. You could still copy and paste the text block to reveal the original contents.
Wow, it took me a minute to figure out how his entry works. You really could read that code and assume it was correct. The resulting image is perfectly redacted visually, and the missing data is not appended or hidden elsewhere in the file. You would only discover it by inspecting the PPM image in a text editor. Very sneaky!
screenshot - im not convinced apple does not use invisible watermark to add info into image data. but for fact every photo you take with iphone, contains invisible watermark with your "phone serial number". to remove such watermarks, facebook is converting every picture you post for last 10 years... just weird extra con to using modern technology.
try to copy banknote on your printer, it will not print anything, just says error.
+ every page of text printed contains barely visible yellow marks containing again serial number of printer.
There was also the Android (and iOS?) truncation issue where parts of the original image were preserved if the edited image took up less space. [edit: also see replies!]
Knowing some formats have such flaws (and I'm too lazy to learn which), I think the best option I think is to replace step 6 with "screenshot the redacted image", so in effect its a completely new image based on what the redacted image looks like, not on any potential intricacies of the format et al.