Yes. You can take screenshots of pages which require a user name and password to login before viewing the page.

For a form-based login on the web page itself, you will need to create a login profile for the URL on the new screenshot test page. For basic or http authentication, either include the correct syntax in the URL to test, or use the login profile option to have it created for you when creating a new screenshot test.

For a step-by-step guide, take a look at our blog posting:
http://crossbrowsertesting.com/blog/cross-browser-checks-pages-behind-user-name-password.

For more information on issues that may occur, see the following FAQ and scroll to Login Forms or Basic Authentication:
Why do screenshot tests fail or return unexpected results?