I saw the images you are concerned with, and “#content .wp-caption img,…” is what is causing the issue. Specifically, what I posted above. 🙂
After you make the entry to your custom style sheet and save the changes, you may need to log out and clear your browser cache completely in order to see the changes. Your browser caches the style sheet, and may not show the update until refreshed. Ctrl+F5 might do the same thing, without having to clear the cache manually.
If you don’t have any luck using the custom css feature of the theme, as a last resort you could edit the actual weaver II style sheet. (although you should not have to with that theme)
You will find this on lines 1625-1634 in the style sheet