Collect images and write labelling rules

Download Hard Hat Workers from Roboflow Universe. Collect 50–100 of your own images (site photos with permission, or openly licensed images) plus ~10% images with no people (backgrounds reduce false alarms). Write labelling rules before labelling: 'helmet' = hard hat worn on the head; 'head' = head without a hard hat; a helmet in someone's hand is NOT labelled; draw tight boxes; label if at least ~30% is visible.