Nothing has stopped you from taking a screenshot of a funny moment in a FaceTime video call before, and nothing probably will. In fact, Apple has made it even easier — and more lively — to take FaceTime screenshots on your iPhone.
Unlike Snapchat and Instagram, FaceTime does not have any regular screenshot restrictions. This means that whenever you take a quick screenshot of a friend or family member using your sleep/wake and home buttons, they won't receive a pop-up warning saying you did so.
Better yet, Apple included a Live Photo shutter button directly in the app, so regular old screenshots will be a thing of the past. Why take a static image that likely missed the moment you wanted to capture in the first place when you can see a tiny video of the moment instead?
Just like a regular Live Photo, a FaceTime Live Photo captures a second or two of video before and after you press the button, so you'll never miss anything good. And while there are no alerts when you take a regular screenshot, when you take a Live Photo, iOS will alert the other user, just like on Snapchat and Instagram.
In order to take FaceTime Live Photos, both you and the other caller need to be running iOS 11 or using macOS High Sierra. Also, if using iPhones, they must support Live Photos already, which means iPhone 6s or higher. By default, this feature is enabled, so you don't have to worry about turning it on.
When you're on a FaceTime video call and both you and the other person have met the requirements, you'll see a shutter button in the bottom left of your iPhone's screen. Just tap on that during an interesting moment and a Live Photo will be saved to your Photos app, and you'll see a toast message that says "You took a FaceTime Live Photo."
The other user will receive an alert on their display letting them know you just took a Live Photo of them, saying "A FaceTime Live Photo of you was taken."
The photo itself will not include any features of the FaceTime interface, so it's kind of like you just took a snapshot of the other user using their own camera. In early iOS 11 betas, audio was not included in the Live Photos, likely because of laws in some states outlawing recording of phone calls unless all parties agree beforehand. However, in later iOS 11 betas, audio is indeed included. This may change when iOS 11 reaches maturity, though.
While you cannot stop anyone you're video FaceTiming with from snapping a screenshot of you, you can prevent them from taking a FaceTime Live Photo. To do so, go to "FaceTime" in Settings, then toggle off the "FaceTime Live Photos" option. You will still be able to take Live Photos of other people during video calls (unless they have also disabled this feature), but they won't be able to record you in action.
To disable this feature on your Mac, launch the FaceTime app, click on "FaceTime" in the menu bar, and then click on "Preferences." On the next screen, untick the Allow Live Photos to be captured during Video calls box.
If you're running iOS 11 but the other user is not on iOS 11, High Sierra, or using a supported iPhone model, you'll get a "FaceTime Live Photos must be enabled on both devices to use this feature" toast message when trying to snap a Live Photo, and they won't even see a shutter button on their end. So, make sure to hit the "Requirements" section above to make sure everyone is set up right.
If you're both running betas, make sure you're on the same betas too, as it may not work across different beta versions.