Campaign Tracking

Hi All, Our client using the EHP3 and our requirement is Track the campaign response. We are executing the Email campaign to different target group of customer and client wants to know how many people are opened the Email. We are using the mail forms with the content of Images & Attachments. As per CRM standard we can track the response by using “Tacking URL”. But our mail form is not having the URLS. How can we track the campaign response without tracking URL? Thanks, Sri