For example Netflix doesn’t allow to take screenshots, and in discord if you try to screen share the window is black.
I’m sure that other sites do it as well.
In: Technology
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When you develop and app whatever tools you decide to use to develop it you’re bounded to use the provided features an OS provides. One of the features you get access when you develop an app is “events” which occur while an user is using your app. These are “Oh, user clicked <this button>”, or “User just <typed this>”. One of those events is “User just took screenshot”. When that happens you as a coder/developer can decide in your code what to do. You can leave the default behavior which would be taking the screenshot, or decide to do something else. Many apps, especially apps that manage important data such as banking apps (also intellectual property apps such as Netflix) disable screenshots in order to secure the data they use within their apps.
What platform are we talking about? I’m pretty sure you can take screenshots of Netflix or discord on a Windows.
EDIT: maybe they have some hooks installed for the Screenshot button on the keyboard? I rarely ever use that button, since you can take easy screenshots with Win + Shift + S. I don’t think they can stop that.
I think other posters may have missed the question in ‘How’ do they do it, not why, I’m going to try and explain in terms of iPhones (this is my first ELI5 answer!)
When you take a screenshot pressing the button tells the app you have open that the user has just hit the screenshot combo of buttons, most apps ignore this but others either record it or even further then throw up something else for the phone to capture.
iOS uses something called views (I’m not an expert, only started learning last week!) which presents the information to you on the screen, when you hit the screenshot button something called **.UIApplicationUserDidTakeScreenshot** is passed to the app, the app can then use that notification to temporarily show the user a different (blank) view for the screenshot, before continuing on as normal.
There is probably other calls like this on other platforms like Windows, Android etc
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“[…] the manufacturer of the device on which you are watching the content is cooperating with the service provider […]”
https://www.quora.com/What-technology-does-Netflix-and-other-streaming-services-use-to-prevent-someone-from-screen-capturing-a-movie-or-even-taking-a-screen-shot-I-am-a-Computer-Science-major-and-its-annoying-me-that-I-cant-figure-out-how-it-works
Other source:
https://apple.stackexchange.com/questions/316096/how-to-screenshot-netflix/316097#316097
On the Android app Netflix is set with FLAG_SECURE
“The flag treats the content of a window as secure, preventing it from appearing in screenshots or from being viewed on non-secure display”
https://developer.android.com/reference/android/view/WindowManager.LayoutParams
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