The NeedService image is located at
/Firmware/all_flash/all_flash.(MODEL-NAME).production/(needservice.(cpu).img2/3 in the IPSW. The NeedService logo is flashed to NOR (or a functionally equivalent partition). It is probably displayed when a hardware fault is detected.
NeedService logo as it appears on iPhone OS 1.0:
And as it appears on iPhoneOS 2.0 and 3.0. (Removed in 4.0)