F - Cached Static Content

I’m getting an “F” for cached static content.
WARNING (1.0 hours)

How can I increase my grade?

Set your expires headers for > 30 days for static content. You need to understand the ramifications though and make sure your site is designed with long caching in mind (versioned resources in particular - you can never change a file without renaming it).

Thank you for the reply. I changed it to 31 days and now I have an “A”.
My web site is an e-commerce web site so all of the static images will not change.

The product images are stored in the database as byte arrays and saved to disk in a different directory.