Browsers include a setting for those with a slow Internet connection which disallow automatically downloading pictures. You may have changed your setting in the browser options. For whatever browser you have, Verify that the Show Pictures option has not been turned off.

Enable scripting, ActiveX controls, cookies, and Java programs
it may well be that you don't have Flash installed (check it here http://www.adobe.com/products/flashplayer/ )

If can also happen with some firewalls if they are configured to block certain content from certain sites....

...Right Fishprince?