Remove the Login Screen Icon

This might be an easier way to do what you want.
found here: Only show user and password text boxes on Windows 7 Logon Screen (hide usernames)

Start -> Run
type: secpol.msc

Navigate to Local Policies
Select Security Options

On the right hand side locate: Interactive Logon: Do not display last user name

Enable this feature.

Now your user icon will not appear. Done.

akhenax said:

This might be an easier way to do what you want.
found here: Only show user and password text boxes on Windows 7 Logon Screen (hide usernames)

Start -> Run
type: secpol.msc

Navigate to Local Policies
Select Security Options

On the right hand side locate: Interactive Logon: Do not display last user name

Enable this feature.

Now your user icon will not appear. Done.

Just tried this and my picture still shows up on the login screen