A lot of us are already used to Windows 10 and ways of making screenshots while actively using the device. Examples of such tools are Greenshot and windows inbuilt snipping tool etc. Windows 10 has two screens to navigate through before getting to the desktop (logged in).
The first is the locked screen and the second is the login screen. Taking a screenshot of the lock screen is relatively easy. Here is the step in taking a screenshot on a locked screen.
Print Screen (PrtScr) key After successfully logging in, use the Ctrl + V on your keyboard to paste it in Paint or app of your choice. But Making a screenshot of the login screen is relatively not very straightforward. When I encountered this issue, trying to take a screenshot of the login screen, here are the steps I followed to ensure I am able to use the snipping tool on the locked and login screen.
Click on Run, and enter regedit and press enter to open the Register Editor
HKEY_LOCAL_MACHINESOFTWAREMicrosoftWindows NTCurrentVersionImage File Execution OptionsCreate a new Key and rename it
Rename the new key created to utilman.exe 
Create a new String value called Debugger at the right panel. Then set the path of the snipping tool (see below) as the value of the string
C:WindowsSystem32SnippingTool.exe
This completes the tweak to get screen capturing to work on the login screenshot on Windows 10.
To test this, perform the following steps below.
– Navigate to the Login Screen. Click the Ease of Access button, the snipping tool will pop up.
– Take the screenshot of the Login Screen and
– Click on the copy button to copy it to the clipboard.
Note: At this time, you will not be able to save the screenshot yet, until you are logged on to the desktop.
Now launch any of your favorite editing tools such as Paint app and paste it.