Well, I'm wondering why you want to use public key encrypted (SSL) connections for your pictures?
HTTPS is a secure form of HTTP using a public key encryption algorithum which would require setup of a certificate on the host server, i.e. your picture server. It's normally a method to secure transport of transactions and not for simple load of pictures.
I would assume ebay doesn't see the need for secure connection to a picture server and therefore doesn't recognize HTTPS as valid for the URL entry.