You can make items appear float or stuck between partial blocks

you can place two slabs vertically to create a small middle gap, then place an item frame on the bottom slab's top face and another on the top slab's bottom face, both fit stacked right in that space. Use invisible frames with 

/give @s item_frame[entity_data={id:"minecraft:item_frame",Invisible:1b}]

(remove the symbol between@s when pasting or write you username instead of @/s )

works with other partial blocks horizontally as well, like cake, honey blocks, trapdoors,decorated pots, and shelf