forcing browser to cache images in php website

I've a php based website and would like browser to cache the images for 30 days .. i am using a shared hosting solution where I do not have access to apache config to enable mod-headers or other modules and so can not use ht开发者_开发知识库access mechanisms for this.

my site is a regular php app, and has both html contents and images. I would like browser to cache images only. I've seen php's "header" function, but couldn't find a way to force only image cache .. How do i go about it ?

Thanks

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As far as I know, if you can't get access to Apache to set the headers, your only other option is to serve images from a PHP script so you can use the PHP Header methods to set the headers.

In this case, you'd need to write a PHP image handler, and replace all your image tags with calls to this handler (e.g. http://mysite.com/imagehandler.php?image=logo.png). You would then have you imagehandler.php script retrieve the image from the file system, set the mime type and cache control headers, and stream the image back to the client.

You could write your own, or if you google, you will find image handler PHP scripts. Either way, make sure you focus on security - don't allow the client to retrieve arbitrary files from your web server, because that would be a fairly major security hole....