The hole that the rod goes through to hold the brake in the set position is probably wallowed out, preventing the pedal from holding. It works like the little sliding prop on the cylinder rod of a screen door.
I just looked at mine for comparison and you can't see any light or space between the pedal rod and the stop. Your hole looks slightly larger than the pedal rod.
Have you adjusted your brakes and parking brake as specified in the shop manual?
Also, are your drums new or worn out. They may be worn beyond spec for the brake to get a good grip.
