u/-Lastered

If you make map art over the void (like in the end) and place glass above the void, those map pixels will be transparent. For the block to be visible underneath the item frame does have to be invisible though.
I took the crate texture from this recourse pack (by Samey the Hedgie) and used MapartCraft to create map art for it.
Then I destroyed the parts of the map art that would be transparent and added glass underneath.
I like this approach over using just a resource pack because you don't lose any existing Minecraft textures and you get to experiment with different blocks under the crate texture.

I'd be interested to see if anyone else has used a similar technique for anything else