When you want to post a shot from flickr, go to "Actions" option above the shot, then choose 'View all sizes' choice. From there choose which size of the shot you want to post, when you choose the size then just click the right click of the mouse on the download this photo depends on the size and choose "Copy link" from the mouse choice box, it will give you the direct link of the shot ended with .JPG extension, this is what i always need to post anything on any website, then from the forum here you choose the image icon and paste the link of the direct flickr link of the shot.
I think you managed to do it right, but i don't know why people always have problem to post images from flickr, also before you post anything here check the preview post to see if your shot will appear or not.