problem of picture flashed on using Timer control

When I am using a timer control to updated the panel frequently, there is a problem as follow:

The picture which is in the Update Panel will flash and refresh when the timer ticked.

How can I reslove this problem?

I want that if the imagebox's imageurl isn't modified, the picture don't need to refresh.

When you use a Timer to trigger an UpdatePanel, the UpdatePanel's innerHTML is refreshed each tick even if there are no changes to it. If you want to only refresh the panel when there are changes, you might consider usingthis technique to poll the server for updates and only refresh the UpdatePanel if need be.