How to fresh the content from web server automatically

Currently I'm designing a system web interface and I'm facing a problem.

Say, via the web interface, I controlled the system, generated a new pic and saved it to the web server's directory. And via the web browser, I want to show the new picture. But what I could get is the old pics on the server. If I want to get the new pic, I have to refresh the web server(like to restart it, or some other ways to let the server fresh the content).

So my question is how to fresh the content of web server automatically?

Hope I clarified the problem. Thanks in advance!