This is a guide to make item frames invisible which can make some good decorative items on the server.

Firstly, you need to make a night vision potion. This is crafted with a nether wart put into a brewing stand which creates an awkward potion.Next,you need to make a golden carrot made by surrounding a carrot with golden nuggets in a crafting bench. Put this into the brewing stand and you will have basic night vision potions.

You then need to craft a fermented spider eye made by putting a brown mushroom, spider eye and 1 sugar into a crafting bench. Put this into the brewing stand with the night vision potions and you have invisibility potions. You will need to extend the basic duration to 8:00.This is done by adding 1 Redstone dust and hey presto, we have the potion we need.

Finally, place your item frame down and add the item in it. Right click with the extended potion in hand and you now have an invisible item frame. Pictures for all these steps linked below.

One example could be a sword on an anvil or a flower like I have at a grave.