Allowing Browser to cache images.

[Anon]

I have found plenty of articles and information telling me how to stop pages being locally cached by the client. My problem is the reverse, I am storing images in the database, and accessing a php file in the <img src='image.php'>. I really don't want the enduser to have to download the image unless it is different. Are there headers I should send to tell the browser not to reload, even if it is only for this session.

thanks

len.