this post was submitted on 11 Mar 2024
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Thanks for your advice. I am a programmer by craft so I can definitely do that. I think the only issue may be books with any important content that is not text, i.e. graphics and images (and unfortunately, many of the books I am interested in have that). If I understood what you said correctly.
Pymupdf has options to handle images. Good package.
But then those images could contain the very fingerprints he's trying to avoid
You can mess with the levels to see any hidden watermarks
There are so many ways to encode information into an image without changing its look that I doubt you'll find most of them by "changing levels"
I'd personally be a lot more likely to blur and add random noise, then use lossy compression if I wanted to mitigate steganography, but even then, they don't need to encode a lot of information and they have a base image and secrets to compare to. It's entirely possible for them to have chosen something reasonably robust through random edits like that.
But what transformations are they stable to?
Theoretically, yes. Handling of images programmatically could allow for some simple lossy compression which would help.
gImageReader or ocrmypdf will get you the pdf text, but after the text will need fiddling with and cleaning. Use LibreOffice, languagetool, write-good, etc to make finding the oddballs easy.
pdftk is what you want for editing pdf metadata.
Gimp is what you'll need for editing images, Looking for watermarks, smoothing edges, lowering quality, introducing random noise, etc.
exiftool is what you'll need for image metadata. Or take a screenshot, add a bit of noise or de-noise, and add back to the new pdf.
Scrivener or LibreOffice if you want to polish/republish, though that's a ton of work.