Pic the size picture you want in flickr, small, medium, or large and right click on photo. click properties and copy the link in the pop up next to "address" "URL". Next click the insert image icon above reply box(6Th from right) and paste your link. image embedded! have fun
Click the Share this button above the image
Select the "Grab the HTML/BBCode" option.
Make sure to swap to the BBcode option, listed below the drop down for picking size.
Select the text, copy and paste to thread.