[StarBuG]

If you simply want to resize images via CSS then add this to additional.css Template:

.postbit .content img, .postbitlegacy .content img, .postbitdeleted .content img, .postbitignored .content img, .eventbit .content img {
max-width:XXXpx;
}

where XXXpx is the max. width you want the image to have.
You can either use px or %.