Did you…print out a screenshot of your phone?!
*added for clarity.
A “watermark” is simply a version of that designed to be invisible or imperceptible to the human eye, for example by embedding information in the least significant bits of the pixel colors.
“Digital Watermark Steganography” is a good search term for further investigation. As is the case with many security topics, there is an ongoing arms race between technology used to hide information, and technology used to detect information hiding.
At the end of the day if you truly wanted to share a screenshot of the iOS settings UI and remain anonymous, you should probably consider just drawing it with crayons. Except then someone will come along and process the crayon marks to recover your fingerprints etc. etc.
In this case however, it's hard to imagine how you'd do this without being detected. If you loaded the screenshot into mspaint and used the paint bucket tool, any color differences will become apparent. You could limit your modification to the edges, but detail there is going to get wiped by jpeg compression (if any).
Another example; most printers covertly embed an identifier in their prints.
I have a vague memory of a pre-release video game doing it? Or maybe it was just debugging information that they were embedding. shrug
Personally I don't believe Apple is doing what you describe (though maybe they might do it to a prototype iPhone). But it's certainly your right to hold that belief and take measurements to protect yourself. Shame you're getting downvoted for explaining yourself.
EDIT: Fixed a typo; thank you.
This frustrates me a lot with my current printer. The yellow dots which "covertly" identifies my prints are way too visible in the print. So every time I look carefully at something I print I am reminded of how I am being watched.
To be picky only colour printers, at least officially (though there are theories about similar ID for B/W laser printers):
Something that actually protects your privacy (and doesn't make you stick out like a sore thumb) is getting the screenshot from an image search and posting from a regularly rotated HN account, all the while using tor.
The main thing I would worry about is actually not Apple; instead (1) what information might Apple hide in plaintext in the image that a third party could extract?; and (2) what identifiers might there be that a third party could use to correlate multiple images as being from gorgoiler’s phone?
But honestly it just feels odd to upload a screenshot without doing something to scrub it. I find it helpful to practice good security even when, as you point out, the probability of it being necessary is very low.
A lot, actually. But why Apple would take the engineering resources to implement this, and risk all the reputation damage? If they're doing it for the money, how would they monetize it? If they're being coerced by the government, what's the government's motivations? In both cases, is smuggling bits in screenshots really the most plausible way to do it? Surely there must be some better way stenography in screenshots?
>But honestly it just feels odd to upload a screenshot without doing something to scrub it. I find it helpful to practice good security even when, as you point out, the probability of it being necessary is very low.
On the flip side, if you do unusual obfuscation of your uploaded image (eg. heavy post processing), that in itself is an identifying characteristic. You're going to be that guy who uploads his screenshots in greyscale, with heavy compression and blurring. https://xkcd.com/1105/
e.g.: if you use an encrypted chat app ONLY after a murder occurred, then this would be suspicious. If you always use encrypted chat apps, then there's no information hint being given about your possible involvement with the murder.
Are they actually incapable of learning the right way to do things? Is neuroplasticity playing a role here? Do they not care that their images look terrible when zoomed in on? I guess they grew up in an era when photos frequently had time and date stamps, and if their eyesight is going... I guess that explains both points.
I thought some apps and iOS had already responded to this workflow by doing smart things when users try to create screenshots. If they haven't yet, they should. There's no need in the common case for "screenshot" and "share main image" to have different UI entry points. Just pop up a menu asking the user that they want when they push the button.
No.
Or I can just hit two physical buttons on my phone and grab the image in the form of a screenshot. Because I don't care about the image fidelity, I usually just want to share the thing on Discord or Slack or wherever.
Don't be so arrogant as to assume that people doing things differently than you must be too stupid or old or blind to do it "the right way".