Browse into the Exchange Installation location
\V14\Client Access\OWA\<version number>\themes\resources
Every .gif file inside this folder serves its own purpose
Am going to customize a little
For Example :
Open : lgntopl.gif
Take a backup of that file
Just edited it and replaced the file in the below location
\V14\Client Access\OWA\<version number>\themes\resources.
Now Look at my OWA page
Quick reference in TechNet on which .gif serves which Purpose
http://technet.microsoft.com/en-us/library/ee633483.aspx
Regards
Satheshwaran Manoharan
Maheshkumar S Tiwari edited Original. Comment: Added tags