This is not a feature of osTicket at this time.Also I do not feel that it would be particularly safe to have the server go and grab an attachment from some where else to embed in the ticket.  This sounds like a great way to introduce cross site attacks, viruses, etc. into the system.  So I highly doubt that such a feature would ever be added.  If you want the attachment in the ticket, people should attach it to the email, or add it via the ui when they create the ticket.