Here it is!

As some may know, Item Frames use five Elements in their model;
Four for the wooden frame, and one for the leather background.

Well, I edited the model file they use to only have one Element;
One for the Leather and the Wood, combined.

Since they're all on the same level, the wooden frame is no longer poking out. This results in a slight change in how Item Frames look:
With vs. Without the pack.
As you can see, it's just a change that isn't very noticeable.

I have observed the framerate going up whilst using this resource pack in an Item Frame-heavy area.
 
Edit: URLs.