Delete all files in:

C:\ProgramData\Microsoft\User Account Pictures

%appdata%\Microsoft\Windows\AccountPictures

Create transparent picture 50x50px, name it and save it to the:

%appdata%\Microsoft\Windows\AccountPictures

Now open the registry editor and navigate to:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\Explorer

In the right pane right click and choose Add DWORD (32 Bit) Value
Name it UseDefaultTile. Double click this new DWORD and set its value to 1.