Changing the default images for sap portal 7.3

Hi ,

we are on portal 7.3 and currently working on changing the look and feel as per the customer branding standards and the requirement is to change the standard images like the ones under  Ess, Mss,content admin, user admin and various others roles there on the portal , please assist me how we can achieve this level of customization .I know how to change a standard image but role specific i am not really sure

Thanks