Dynamically Update Email Templates

All our message templates include a company logo. When that logo changes, we have to go into each message template one by one to update the logo. It would be better if we could add the logo as a resource, perhaps in the resources area, then use a URL to link to that image. The URL would never change so the message template only needs to be updated once during set up and any time the logo changes in the Resources, the email templates will all automatically update.