First you need to make sure what program is installed with Face Recognition. It's usually located into the system tray. If it's necessary, try disabling the application first (you may need to use an unlock password) then you can try to disable it from the Add or Remove Programs menu.
If you encounter errors, you can try to force the uninstall operation using an application developed for these situations. Try using Revo Uninstaller. Even if it can't uninstall the application normally, it will force it to uninstall by wiping out all traces of its presence from the system.