To post picture of toilet seat: <img src="http://www.somesite.net/path/image_file.jpg">
For example, this image is posted by entering <img src="http://www.plumbingstore.com/images/toilet-seat-1900ccp.jpg">
If you're using Internet Explorer, you get the URL by right-clicking on the image you want, then selecting "Copy Shortcut" from the popup menu. After you type the <img src=" you just press Ctrl+V to paste the copied link into your text, then finish with ">
One warning: There are sites that don't like you to link their images. If you get one of those, the actual image posted to FR will not be the one you intended. It will usually be some kind of warning not to link their images. However, most news sites don't have any restrictions on linking.