How do I bleed a very old radiator and identify whether my system is steam or hot water?
That's hot water. Not a great picture, but there's a circulating pump barely visible, as well as the other factors you have noted.
In your second picture, the bleed valve is the black thing to the right of the water inlet, on the corner. Takes a flathead screwdriver as best I can tell from the picture.

There's also at least one automatic bleeder visible at the boiler.

If you have children, you will want to clean up the peeling white paint, which is very likely to be lead-based.