Find the correct partition by using root explorer and navigating to /dev/block/platform/. Should be only one folder there, and then /by-name/. So the command should be
dd if=/sdcard/system.img of=/dev/block/platform/YOURFFOLDER/by-name/system
I maybe wrong in the spelling so check it with root explorer.
It did read but now the phone is stuck and not booting anymore :(
I did the recovery, but the update.zip which was stored in the phone is the G firmware which the phone is not accepting and it says firmware corrupt.
How to flash the software to recover the phone?