Below we will see how you can take a snapshot or screenshot of the Windows 10 lock screen.
Since Windows 8, there's been this feature that displays a separate lock screen. When your computer is locked, a full-screen image appears instead of the login screen. It's an extra screen that appears with a background and some useful information, like the clock and date. It appears before you can select a user account to log in to. 
With Windows 10, Microsoft added the Spotlight feature. Spotlight is a feature that allows you to have a random image on your lock screen every time you turn on your computer.
If you like any of these images and want to take a screenshot of the lock screen in Windows 10, follow the steps below.
Before you proceed, make sure you’re signed in to your account in Windows 10. Windows 10 comes with two lock screens. The first one appears when you’re signed in to your user account and your account is locked. The second one appears when you sign out of your user account. It’s called the “default lock screen,” and it appears automatically when your computer has been idle for a certain amount of time.
To record your personalized lock screen, once you're logged in to your user account, lock your computer and do the following:
Press Win+L keys together to lock your computer. The lock screen will appear.
Press the PrtSc/SysRq button on your keyboard.
Press Enter key to close the lock screen and log in to your account.
Open Paint and paste the screenshot from the clipboard.
You're done. The lock screen screenshot will be pasted from the clipboard.
