Many email clients will not display images automatically unless the recipient has told the program to allow them to be displayed. There is a very good article on this topic at: http://www.campaignmonitor.com/blog/post/2559/current-conditions-and-best-pr-1/
Constant Contact does not support Outlook 2007 so it arrives without pictures. With more and more business using Outlook 2007, this is something that Constant Contact needs to address.
Kiwanian - the problem is with M$ not CC. When M$ released Outlook2007 they reverted back to a very old rendering engine for HTML - and basically "broke" HTML emails. You can learn more at the Email Standards Project: http://email-standards.org/