There is no image for he original Aura since the internal storage is not removable. However several people managed to use the external SD card with the original Aura H2O image. See
Factory .img for Kobo Aura (N514) for a bit more information. If I ever knew the button combination to boot from the external SD card, I no longer remember it.
I'll send a link to the Aura H2O image in a PM.
Edit: PM sent