Windows 7 Login Camera is a nice freeware that lets you capture screenshots of Logon screen very easily.
To grab the screenshots :
Install the application, lock the screen by pressing CTRL + L and use ease of access button located on the bottom left side. Windows 7 Login Camera launches and allows you save the captured screen on desired location.
This handy tool is developed by deviantart.com website user yvidhiatama and it’s compatible with all the 32bit version of Windows 7.
Make sure .NET Framework 4.0 or higher Installed on your PC to use this tool. Download .NET Framework 4.0 directly from Microsoft’s download website.
Download Windows 7 Login Camera here