Normal: the image to use when the jack is enabled and the user isn’t currently interacting with it.
Hover: the image to use when the mouse is hovering over the jack.
Disabled: the image to use when the jack is disabled. When a user is dragging a cable from an input jack, all other input jacks will be drawn in their disabled states, and likewise for output jacks when a user is dragging a cable from an output jack.