Comment by thepasswordis
14 hours ago
It is actually astonishing to me that this is not something which can be turned off at the OS level, or as a permission setting in the app permissions.
The app knowing I took a screenshot feels adjacent to me to a keylogger. Imagine how many apps are capturing that information silently. To my mind, a screenshot is something that is happening outside of the app context, the app knowing about it is a security flaw imo.
> The app knowing I took a screenshot feels adjacent to me to a keylogger.
To my knowledge, this is a misunderstanding. The app does not know that you are taking a screenshot, rather iOS knows you are taking a screenshot (as it must) and is excluding an element on display that has been designated by the developer as sensitive information. This is the same technology that prevents you from accidentally screenshotting your password manager; the developer has simply performed a nifty trick to display a small icon behind where the “follow” button would otherwise be displayed.
There are plenty of instances where this sort of thing can be annoying, such as when you try to screenshot a streaming service app and DRM enforcement leaves you with a blank screenshot, but IMO this particular instance is actually very tasteful; seeing “follow” on every screenshotted post is just useless noise, but a small unobtrusive platform icon is a useful reminder that the post came from Bluesky and not another very visually similar service like X(cancel) or Mastodon.
The app actually is notified after the screenshot is taken: https://developer.apple.com/documentation/uikit/uiapplicatio...
Android does it too: https://developer.android.com/about/versions/14/features/scr...
This prevents us from taking scrolling screenshots (a native feature in many smartphones today that is often useful when there is more than one screen of content).
I dislike this hijacking for that reason and wish there was a way to turn it off.
Spotify uses this and it annoys me all the time.
If you screenshot what you are listening to, after the screenshot is taken spotify will open a full-screen popup to "share" the song you are listening to. This is quite dumb, especially since if you wanted to share a song via the screenshot, you can do so in the OS-level screenshot UI, and then you would close it and see Spotify's own similar version of the same UI. Spotify just really wants you to use their own share button so that they can track you.
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Very interesting! Parent poster is correct, that notification does feel akin to a key logger… although I’m not sure that it applies to this bluesky feature.
So in this instance, am I right in understanding that iOS posts a notification after the user has completed a screenshot, which would make it impossible for the developer to use this notification to trigger anything that would modify that screenshot? Hence the developer’s work around?
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> This is the same technology that prevents you from accidentally screenshotting your password manager
Yes, and I would say it's a bad thing that the OS tries to prevent this.
> seeing “follow” on every screenshotted post is just useless noise, but a small unobtrusive platform icon is a useful reminder that the post came from Bluesky and not another very visually similar service like X(cancel) or Mastodon.
I would say it's a bad thing that Bluesky makes the screenshot look different from what was on screen for the user. If I cared about excluding the "useless noise" from a faithful depiction of the pixels on my screen, I could address that myself.
Why is this feature bad?
As someone who develops apps for confidential conversations, making it harder for people to screenshot the confidential stuff is a feature the sending party wants, that is why they send in your app as opposed to others. It doesn’t make things impossible, just hard enough that 95% of people won’t bother to take a copy.
Same for example with disappearing audio messages on whatsapp
What I don’t like is the app being informed that I took a screenshot. The OS can hide things in screenshots without this.
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> Yes, and I would say it's a bad thing that the OS tries to prevent this.
Another way to look at it is the OS makes certain guarantees to the developer around security. Giving control of this to the user would erode that guarantee from the OS to the developer. The result of that is that some developers would simply never display some information (e.g. due to their own contracts or reasonable concerns about fraud/abuse/etc.).
Very similar to the video pipelines in modern devices. Prior to video pipelines which the OS could attest could not be hijacked by the user, many content providers simply would not allow e.g. Netflix to release their content on certain platforms. That the OS does provide such an attestation option for developers allows uses that otherwise would not exist.
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"The app does not know that you are taking a screenshot, rather iOS knows you are taking a screenshot (as it must) and is excluding an element on display that has been designated by the developer as sensitive information. This is the same technology that prevents you from accidentally screenshotting your password manager"
And that is reasonable, but it is also a surface where an app touches the OS, which should be a permission boundary that I can control. Allowing the option to opt-out of screenshot blocking with a proper double-confirm warning and biometric auth is also reasonable.
The OS notifies the app after the screenshot is taken. The app doesn’t get to do anything in response to it being taken or allow it to be blocked.
They’re abusing an iOS text rendering control function handled by the OS. Before the screenshot is taken iOS swapped out the rendered text for “sensitive” fields and images that.
The replacement is supposed to be something like a masked account number, password asterisks, or just general blur.
Not a marketing logo.
It's wrong. iOS sends an event on screenshot.
https://developer.apple.com/documentation/uikit/uiapplicatio...
Neither of those use cases seem good or tasteful to me as a user, I don't think this concept of "secure (from the user) context" should exist, but maybe that's just me
> This is the same technology that prevents you from accidentally screenshotting your password manager
I should be able to screenshot anything I want, including my password manager. I should be able to opt-out at the OS level, or any other level that enforces it. That's why it's definitely a user hostile feature.
Can Snapchat no longer inform the other user when a screenshot was taken?
can someone just take a picture of the phone with another phone, or use a screen recorder?
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I think bsky's use of this malware feature is as benign as it's possible to get, but it's still a malware feature. As you point out, the real reason this exists is to enforce DRM and make your computer serve Netflix et al rather than the person who owns it.
> accidentally screenshotting your password manager;
I could not think of a more useless justification for installing malware into the OS. Okay, you've accidentally screenshotted your password manager. So what? Are you going to accidentally upload it to the internet too? I'd much rather live in a world where people who are that stupid face minor consequences for their actions than one in which all of our own computers are used against us.
> The app knowing I took a screenshot feels adjacent to me to a keylogger.
That is what this article is about and why you should read it before commenting. The whole point is that it doesn't need to know you're taking screenshots. That's why it's a clever trick.
But for completeness, iOS apps can detect screenshots. That’s what allows them to show annoying popups with a share option when you take a screenshot.
What? App-B on iOS knows when I'm taking a screenshot from App-Y? I don't have iOS to check but that seems crazy.
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but you didn't read the part where the mechanism is explained? it doesn't do anything like capturing information. it just marks a button "sensitive" causing it to be hidden in a screenshot, thus revealing an icon that was put there underneath the button.
Did you read the article? Bluesky doesn't know you're taking a screenshot, iOS just hides the follow button in the screenshot (consequently making the Bluesky logo visible).
iOS does tell the app that a screenshot was taken though
> Please don't comment on whether someone read an article. "Did you even read the article? It mentions that" can be shortened to "The article mentions that".
Found in the HN commenting guidelines, linked at the bottom of most pages
Noted, I'll keep that in mind when commenting in the future.