We are about to deploy Windows 7 in an enterprise environment and I am having some concerns concerning the account picture that is displayed on the logging screen, and in the upper right corner in the start menu :

How do you guys deal with this picture in an enterprise environment? Because I guess that my users will waste some time trying to change this picture, and try uploading their own picture, which is not what we want in a professionnal workspace. And if we deny users to change that image, maybe some people will be mad about the picture that have been permanently randomized for their account.
So is there a way to replace every account picture with a dummy logo of the corporation, or maybe do you have a better idea?