Issue: After installing Exchange 2007 SP3 Rollup 12 the Outlook Web Access logon page is blank showing no images.
Solution: Open Exchange Management Shell and execute the updateowa.ps1 script located in C:\Program Files\Microsoft\Exchange Server\Bin
Conclusion: At this point OWA should be displaying images properly and you should be back in business.
Spot on! Did not encounter this in my test environment, but in production all I got was a blank page. Previous IT company left me with a SP1 UR5 install, so made a big jump to SP3 UR17 :-)