Keep images from spilling out of the center column

I'm updating a website for a very small community where the residents are encouraged to post about their events and, well, anything. Many of the authors are NOT web savvy at all. So I'd love it if someone could suggest a way to tell Atahualpa or Wordpress to automatically make images fit within the center column.

If you go to the development site, you can see what's happening with the images. Link to development site

I know I can go into the post and reduce the image size, but there are over 600 posts in the archives and MANY of them have images that are too big. Plus, like I said, many of the contributors aren't savvy enough to resize their images every time they post. So, I'd LOVE, LOVE, LOVE it if someone had an elegant solution for me!

TIA ~ Laura