If you want them as url's, you don't even need the URL tag if you're just having them as a url without a name.
For instance,
http://www.pixspot.com/albums/userpics/ ... bridge.jpg
will show up completely fine as a url, whereas you the URL tag applies to a block of text that you'd like to hide a link in.
You just, select that text, press the "URL" button, and where the tag says "[ url ]" you enter "[ url=http://www.pixspot.com/albums/userpics/thumb_Bells%20bridge.jpg ]" or what have you. Check to make sure that at the end of the text you want linked, there's a closing tag. That's one of the "[ url ]"'s with a "/" before the "url".
If you want to make an image out of it, same logic applies, except for that you write the url of the image in (instead of whatever text you planned), select that url text, and press the "Img" button which will place "Img" tags around your url's making sure those images post correctly.
Edit: I've gone ahead and made your images into "Img" linkers, however, you might want to resize those images on your server into something bigger than a thumbnail. Keep in mind that the maximum you should go is 700 width, but you can certainly go bigger than what you currently have.