rash

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.

If you wish to change these simply replace them with another file up to 128
x 128 pixels in size to prevent it from being automatically cropped to fit the
user picture display box.