So, I put down an item frame, and it is invisible. You can put an item in it though!
Steps to reproduce
-Be sure to open your game fresh. (I'm using a creative map.)
-Place an Item Frame on the wall.
-Place an item inside the Item Frame.
-Press the home or sleep button on your device.
-Return to the game and you will notice how the Item Frame disappeared showing just the item on the wall.