User profile picture GPO is not working

Hi,

recently i created a GPO on server 2008 R2 to apply our company logo to all machines ( win7 & win8 ) in domain, as user profile picture.

after GPUPDATE those images are being downloaded to all domain machines (to C:\ProgramData\Microsoft\User Account Pictures )but, not showing at log on screen/lock screen.

picture specs. are 128x128.
picture location is shared to all domain computers and authenticated users.

MUCH APPRECIATE ANY HELP

Thanks,

Rafi