I have seen some third party utilities that could do this in Windows 10. I have also found that deleting all image files in the following folders would also accomplish this task. Make sure you have backups in the event you wish to restore.
C:\ProgramData\Microsoft\User Account Pictures
C:\Users\Public\AccountPictures
%AppData%\Microsoft\Windows\AccountPictures
However, beginning with Windows 10 build 14371 and higher the third party utilities have no effect. Likewise, deleting the images in the folders above has no effect. I cannot find where MS is pulling the user account picture from in these newer Windows 10 builds. Your help is appreciated.