get into flickr and get the proper view size of the image(i like medium), then right click and hit "copy image location". now back on my post i paste the image location i just copied.
next, hit "preview post" and when you get your preview, scroll down to where you can edit it. you will have your image info encased in two sets of brackets that look like this- [url]. simply delete the "url" and replace with "img" so it looks like this- [img]. so now you have your image location book ended by two sets of "[img]" brackets.
hope this helps