Maybe the images are blocked. To unblock images, open Outlook Express and follow the steps:

1. On the Tools menu, click Options, and then click the Security tab.
2. Clear the Block images and other external content in HTML e-mail check box.
3. Click OK.

You can always try to right click on the missing picture and say download pictures. You can also add certain senders to safe sender list.

More information about this problem here.