This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
Lookup the class "ImageButtonBean" in the Struts Javadoc. You will see that if you define properties in ActionForm of this type and assign each property to a particular button, you will be able to tell which image button was pressed.