Headers for PNG image output to make sure it gets cached at browser?

Question

I have images (PNG) that are generated dynamically and will be embedded in websites and forums. When an image gets posted on a very busy page, there are a lot many connectio

Answer 1

The final thing that worked was:

header('Pragma: public');
header('Cache-Control: max-age=86400');
header('Expires: '. gmdate('D, d M Y H:i:s \G\M\T', time() + 86400));
header('Content-Type: image/png');

Now the browser does not make requests for the image when loading a page with embeded one.