Here is a link to the Hobbit box set. It will not work in this message board to put in the URL for a picture on flickr, because that URL is actually a web page, not a specific, individual graphic like a jpg or gif file. BUT you can put, as a link, in the message, the URL and then someone can click on the link to get to the picture. Or if you can put the picture or graphic on a web page that you control, then you can put the exact URL for that graphic only in to the image box when you post your method - it would look like
www.junious.junior.com/image.jpg or www.yourwebpage.com/picture.gif etc.
Also you can use the PREVIEW button to see if the graphic is displaying or of the link works.

When you put in a Optional Link URL, make sure you either copy in only the part of the URL after the http:// from your browser or delete out the http:// and then copy in the entire URL from your browser where the page is you want to link to - otherwise you get something like http://http://thispage.com/example.htm and the duplicatation of http:// will screw it up.
Hobbit glasses on flickr