All we know we can specify a cache validator for images by adding following lines to .htaccess file:
<IfModule mod_expires.c>
ExpiresActive On
ExpiresDefault "access plus 1 year"
</IfModule>
.. and ..
<IfModule mod_headers.c>
<FilesMatch "\.(bmp|css|flv|gif|ico|jpg|jpeg|js|pdf|png|svg|swf|tif|tiff)$">
Header set Last-Modified "Mon, 31 Aug 2009 00:00:00 GMT"
</FilesMatch>
</IfModule>
But, it will be effective for real JPG or PNG files. However, the question is, how to specify cache validator for images that are built with PHP codes and imagejpeg/imagepng functions on fly? (above codes are not effective for them)
P.S: I have tried to simulate the URL of image created by PHP like a real image using .htaccess file (e.g: http://example.com/1.jpg, which is generated by PHP file and is not a real .jpg image), but still receiving cache validator warning.
You can add the PHP code before imagejpeg/imagepng functions:
function TestModifiedSince($PageTimeStamp, $TextDatePage) {
if (isset($_SERVER["HTTP_CACHE_CONTROL"])) {return;}
if (!isset($_SERVER["HTTP_IF_MODIFIED_SINCE"])) {return;}
$TestTime=strtotime($_SERVER["HTTP_IF_MODIFIED_SINCE"]);
if (($TestTime - $PageTimeStamp) >= 0) {
header('Last-Modified: '. $TextDatePage, true, 304);
exit();
}
}
# hh mm ss MM DD YYYY
$DateUpdateBaseDef = mktime(00, 00, 00, 08, 31, 2009);
$TimeHeadUpdate = gmdate('D, d M Y H:i:s', $DateUpdateBaseDef).' GMT';
TestModifiedSince($DateUpdateBaseDef, $TimeHeadUpdate);
My idea, make change on server configuration, to execute different extension rather then only PHP. for printing images when you use img tag with source of php file to render image. use different extension such as getimage.iphp. Include in your .htaccess settings with cache control of file with extension .iphp
Finally use header inside your image generation function to set expiry of individual image file.
Its bit theory but might be useful as idea to implement.