Not in the registry that's been found so far. But you can do the
following. In Windows Explorer, go to:
Documents and Settings\All Users\Application Data\Microsoft\User
Account Pictures
Documents and Settings\All Users\Application Data\Microsoft\User
Account Pictures\Default Pictures
In each of these folders, highlight all of the BMP files and right
click. Select Send To, Compressed Folder. Then you can delete the
BMP files. The Compressed folder is just in case you want to restore
them later.
Log off/Log on, and the picture should be gone.