Some times you may be required take a screenshot of windows 7 login screen, in such cases there is no way in windows you can do this neither the windows default print screen button works on welcome login screen in windows. Taking screenshot of the login screen is not possible unless you are running windows in virtual environment using Microsoft virtual pc, vmware or using some other tool.
Win 7 Login Screen Camera is a free tool for you to capture the login screen, and save it as a BMP image file , by clicking the “Ease of Access” button on the bottom left side of the login
screen, Please note that this utility might work on some other earlier versions of windows including vista and xp.
This application works on 32 bit version of windows, and you can save the it to any custom location in windows folder. Ease of access button is located on the left bottom corner of the login screen, below is screenshot or ease of access icon which might help you recognize it.