it's not working from flickr because it's a html page rather than an image. If you right click the image, and choose properties, then you'll see the link to the actual picture. Copy that and put it inside the [ i m g ] tags.
example:
http://www.flickr.com/photos/chrisdono/3553408423/
the picture is:
Code:
http://farm3.static.flickr.com/2469/3553408423_ca39a0da3d.jpg?v=0
so you remove the ?v=0 bit and put the rest inside the [i m g] tags
You can also click on the "all sizes" link for the photo, then choose which size you want and it'll give you a link to paste into your browser for linking to the image directly.