Hi jaikumar,
In our case, our APM logon/logoff/error pages are all fully customized from the ground up under Advanced Customization. At any rate, I opened a case and was advised that switching out the image files at the file system layer is not possible. We attempted to replace the images at both of the known folders, but the original image still remains cached for some of the pages (logon specifically).
I have been told that I will have to manually go through each access profile and assign the new image in order to make sure the mechanisms in place treat the image properly.
Thanks!
-Cory