It's not so much that you can't post images, it's how you post them.
Either you use the image-pasting-button and use the direct URL and paste it into the popup that comes on when you click the button. Or you use the IMG-tag-enclosed URL and paste that directly into the text field.
Or, like some people like to do, if you use the fancy-editor (default) and just drag/drop images into the text field from another browser window.