Are your web apps in separate ear or war files? If they are I bet the server is randomly choosing one of the deployments to pull images from. If the apps all have the same security domains and realms, i suggest putting them all in one ear, with one war and separate jars. I have done this and have had much success!!
Each application is deployed as a WAR. Each has it's own JSP's and images. The system is designed to allow developers to hot-deploy their applications without affecting others. Wrapping up as an EAR may be a work around but requires the Application.xml document to be manually kept in snych...
I think that this should work and, 'random' is not a good thing in a live environment ;-)