This names the FSM state this specific Image object was in immediately before its current one. An admin can compare this to the current status to see whether this stored image's validation workflow just moved forward normally or is looping back to a state it was already in, which would indicate a repeated validation failure on this specific file. If the previous state and the current state are both 'Validating' after a retry, that pattern points to the checksum or format check itself repeatedly failing for this particular image.