Webpage Images Disappear after Inactive Period

We are looking for GWT and java programmers to help us solve a specific issue.

The webpage uses GWT, is written in java and uses a number of javascripts. The webpage content and html is collated by a database stored procedure called by the java code. That content includes image tags which retrieve images from the database [not from a hard drive].

When the user first goes to the page the images are reliably presented on the page and we have established that the java is calling the database to retrieve them. Subsequently, when the user refreshes the page we have established that the browser is presenting images from its cache - the images render very quickly and there is no call made to the database stored procedure to retrieve them.

However, if the page has been inactive for some time and the user refreshes the page many images fail to appear on the page. We have established that no call is being made to the database to get the images. Accordingly, it would seem the browser is failing to get the images from its cache.