Different logo in email than on web interface?

Is it possible for the logo in the email to be located at a different URL from the logo that shows up in the web interface?

In my use case, my web interface uses SSL with authentication required for access, so the image URL is https://.../upfiles/logo.png. I want to serve the logo from https on the web interface because otherwise browsers will complain that there's a mix of secure and insecure content being delivered.

On the other hand, when an email goes out, I want the users to be able to see the logo without having to authenticate with the web server. That means that the URL for the logo would have to be different a different location that doesn't require authentication.

(Alternately, is there a way to tell apache that authentication is not required for location /osqa/myproject/upfiles/logo.png, when authentication is required for /osqa/myproject