Best method to serve a dynamic image for mails

I would like to represent dynamic images in an email. For example with the given url

<img src="http://myserver.com/index.php/user_key/thispagestate.jpg" />

I would like to serve a different image based on logic within my server. There will only be between 2 to 4 static images used to represent the result of any given request.

The 2 options I had in mind were:

1. to serve the images directly using perhaps imagecreatefromjpeg
2. Or generate 302 redirects

Seeing as each request will result in one of a limited number of images I thought a redirect might save resources on our end and make use of caching on the user's end too. The resu开发者_如何学运维lt for each request will change depending on the user and time, perhaps using redirects will have some consecuence for SEO or spam filtering?

Your opinions on the best method will be appreciated

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The 2 options I had in mind were:

1. to serve the images directly using
2. perhaps imagecreatefromjpeg Or generate 302 redirects

I'd go with #1 in this case, though since it's a static image you can simply use:

header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past
header('Content-Type: image/jpg'); // or image/png, etc.
echo file_get_contents($image_path); // where $image_path is the path to the image
exit;

instead. You'd only need to use the GD functions if you're were trying to do something like adding text on top of the static image.

Note in this cache I'm setting it to cache expire, since the URL will be the same, but the content might change. This could potentially confuse caching systems.

Seeing as each request will result in one of a limited number of images I thought a redirect might save resources on our end and make use of caching on the user's end too.

The reverse actually, since the same file will now have different content. You'll want them to revalidate the content each time to make sure the proper image shows.