How can I find out if my antique item has any value?

I have two items that I am having great difficulty even finding other similar items or information about.

I have a Cat in the Hat ceiling light cover. I know in many ways ceiling light covers are becoming less common, but I can’t even find another picture of one online.

The other thing is a MC Escher on glass in some steel or aluminum frame. The picture is ‘House of Stairs’ I think.
The glass is placed forward, so when light is on it, the shadow of the picture is on the backboard.
I don’t even know what kind of setting this is called. It’s not a painting, sculpture, or photograph. What do you call pieces of art in this form?

How can I find out more about these things I have?