One way is to have a personal macro to do an action, and then customize the QAT, Select Macros in the "Choose Commands From" drop-down ( that's where it is in Excel 2007 ), click the Add button to add the command to the QAT, and with the command selected in the right-hand pane click the Modify button to choose a suitable button image.
Cheers, Glenn.
Beauty is in the eye of the beerholder.