Normal: image to use when the MIDI jack is enabled and the user isn’t interacting with it.
Hover: image to use when the mouse is hovering over the jack.
Disabled: image to use when the jack is disabled (when the user is dragging a cable from a MIDI input jack, all other MIDI input jacks will be disabled; likewise with MIDI output jacks when user is dragging a cable from a MIDI output jack).
MIDI jacks have a fixed size of 57 x 57 pixels.