(1) Are these missing images found in your Media Library ie. did you upload them from your computer onto WordPress.com servers? And, if so, then are they still in the Media Library? Please check.
Or are the missing images ones you have linked to on some other server somewhere else online such as flickr or photobucket who allow hotlinking?
Or are the missing images ones you have linked to on some other server somewhere else online that does not allow hotlinking?
(2) For details about the options for uploading images see:
(3) For troubleshooting images tips see > http://en.support.wordpress.com/images/troubleshooting-images/
(4) If those do not help then please post the URLs starting with http:// for the posts or pages with the missing images.