What is this hinged metal hardware with an eyelet?
It's a "fangs" style fastener- I use similar styles to hang junk in my cubicle. The teeth latch on to the foam board in my cubicle walls, or it could also be used to grab the foam backing of a picture frame. Found it on amazon by googling "Eye Fastener for Foam Board"

Drytac Push/Pull Hinged Hanger