The ImageIndex property determines which image—from TToolBar's Images list—appears on the tool button. If the toolbar's DisabledImages and HotImages properties are set, different images appear when the button is disabled and when the mouse pointer passes over the button. 

These lists are zero-based; the first image is indexed by 0, the second by 1, and so forth. Since ImageIndex holds only a single integer value, the positions of the selected images must coincide on the different lists. For example, if ImageIndex = 2, the button displays the third image in each list. 

DisabledImages 

HotImages 

Images