There may not be a whole lot of reasons to take screenshots of the login screen on your Chromebook. If you ever need to, however, it’s a needlessly lengthy process. Here’s how to do it.
First off, you need to know how to take a screenshot, which is surprisingly easy: press the Ctrl and []]] keys at the same time. (The “[]]]” key is located above the 6 key on your keyboard’s number row.) Boom, screenshot taken. This part works anywhere—even on the login screen.
The problem comes when you try to retrieve said screenshot because you won’t find it in the default location on your account. Since you’re not logged in when you take the screenshot, the system can’t associate it with an account on the Chromebook.
So where does it store it? In a temporary directory. The screenshot(s) will stay here even after you log in—you just need to know how to copy it over to your account, which will require some time in the Chrome OS shell.
That may sound intimidating, but I promise it’s pretty simple—you just have to type a few commands, and you’ll be rockin’ and rollin’.
So, go ahead and fire up Crosh by pressing Ctrl+Alt+T. Here, type shell and hit enter.
In the shell, navigate to the tmp directory by typing the following: cd /tmp/
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Source : How to Save Screenshots of the Chrome OS Login Screen
