Show frame # in ImageBuilder

I have some sprite sheets with a ton of frames. And for example I need to know the frame number for this "chest" image that turns out is frame 23, so I can use that in script. The image builder currently shows the x/y position of the cursor when you mouse around within the sprite sheet, what would be a ton more useful is the frame idx number of the sprite currently under the mouse, or at least show it when you zoom into a particular frame.