The eMachines boot logo is built into the system firmware. eMachines may offer a tool for altering or replacing that image, but it could vary by model.
I had an old eMachines eMonster 500A that featured the eMachine boot logo and all eMachine's issued mobo firmwares featured it. However I had to dig up a newer firmware issued by the motherboard OEM for it's Napoli-3 Motherboard to make the mobo work with a Radeon VE/7000 card. This was from the Japanese company and not by eMachines, after flashing this firmware on the eMachines logo was gone.
On my current mobo from Asus however, Asus actually has a formal tool where I can add any 256 color 640x480 bitmap to the firmware, but that's a 'feature' from Asus.