Not very sure why the previous one written by fellow bro was missing, I shall start to contribute to this community.
To link your picture from your flickr photo stream,
1. Go to your flickr photostream
2. Select your Desired Picture
3. Go to "share this" **The user interface of flickr has changed a little. Instead of " Share This" it is now a drop down box with facebook icon on the left.**
4. Select "Grab the HTML/BBcode"
5. Select BB Code and the desired size
6. Copy and paste the code to your thread