<p>I'm trying to find the best way to speed up the delivery of the static images that compose the design of an mvc site. The images are not gzipped, nor cached in the server or on the client (with  content expire). Options are:</p>

<ol>
<li>Find why images are not cached and gzipped direcly from IIS6</li>
<li>Write a specialized http handler</li>
<li>Register a special route for static images and write a bynary actionresult method</li>
</ol>

<p>What could be the best solution in terms of performance?</p>

Best solution is to let IIS do it.
IIS6 Compression
- most likely you need to
specify file types to be compressed
like .jpg, .png, .gif types, etc.
Caching will come from making sure that the correct headers are being sent to the client from code, and i believe there is a setting you can set in IIS that enables it for static content, but i'm not sure on that one.