no CMS/PHP scripts please, not in CSS anyway ;) - As I think you've been advised elsewhere this is likely a CMS issue rather than a CSS one. The images aren't even in the source code so CSS can't style them ;)
As a guess (I don't know Joomla) are you using a plugin to detect the first image in article to produce the post teaser image on the left?.. If so it's possibly a setting in that which ignores other images. I'd check out the plugin or it's support area
or if not, it's maybe even just a Joomla setting where you have to explicitly tell it, somewhere in the settings, that you want images in your teaser or intro text.
In short I think you need to be on Joomla support forums rather than CSS ones ;)