I would like to have my centered images have a border whereas no borders for right and left aligned images. Is that possible ?

I believe the left and right aligned images have their own unique class. You could determine what that is with Firebug and then apply the necessary CSS.

try this

.post img.alignright {
	margin: 0 0 0 0;
	padding: 0;
}

Thanks juggledad, it works like a charm...