He is not posting a direct link, just a URL address. A direct link is required unless you just want to post a link to the photo. I can't remember what Flickr offers but I am sure it is just like Photobucket which offers multiple linking options below each picture. One of them is titled "direct link", that's one you want. Copy that URL, go back to your post at APC, hit this button (below), and paste the URL in the window, close and post.