Pictures display when I click on the placeholders but not in the comment itself. This is what I see in the comment notification email:

<img src="http://pics.livejournal.com/run_away_to_sea/pic/0002kxe5"
alt="Two people aloft on a tall ship, one of them in a wheelchair.">

Since the <center> tag works, it's not a matter of HTML being ignored altogether, I think. Try posting a comment using the following syntax to include an image:<img src="http://www.example.net/path/to/image" alt="appropriate text for the image" />(note the final / right before >) with the obvious parameter substitutions. (You can also open a support request since this shouldn't be necessary, I think.)