image URLs missing from posts

Greetings,
I’m trying to fire up a new self-hosted WP instance, and I’m hitting a rather bizarre problem. I add image URLs to posts, yet the images never appear on the main/front page. However, they appear if I view the individual post page. At first I thought perhaps the image was simply not getting loaded for some reason, but when I view the (HTML) source for the page, the URLs for the images are completely missing from the posts. If I go back to editing the post, the URLs are clearly there. This isn’t a theme problem, as it happens with the default theme that ships with WP, as well as a few other themes that I’ve tried.

For example, I have the following in the body of a post”

a
<img class="alignnone" title="VegDal" src="https://foo.org/pix/year3/tygemo/slides/slide_IMG_2148.JPG" alt="VegDal" width="640" height="480" />
b

Yet when I view the source of the main page of the site, all I see is:

a
b

as if that img tag wasn’t even there.

Anyone have any ideas?

thanks