You can find the default pictures of Windows 7 user Account in a hidden folder, path given below. Also you can find Admin & guest account picture here.
•The default Pictures are located in the hidden C:\ProgramData\Microsoft\User Account Pictures\Default Pictures folder.
•The default Standard and administrator account picture is the hidden C:\ProgramData\Microsoft\User Account Pictures\user.bmp file.
•The default Guest account picture is the hidden C:\ProgramData\Microsoft\User Account Pictures\guest.bmp file.
To access these hidden folders you'll need to open up folder options. This web page will show you how:
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