Thanks for asking this question Chrissy, I knew it would come up sooner or later

For security reasons, the forum won't let you use anything but the simplest html. The links that Flickr provide have a whole bunch of useful extra information, like alt text and image dimensions, but the forum doesn't support those. So for the example you had in your post on the games thread:
<a href="http://www.flickr.com/photos/mystic-venus/2874071881/" title="Scenically Wired by Chrissy Downunder, on Flickr"><img src="http://farm4.static.flickr.com/3059/2874071881_5e05fbb707_m.jpg" width="240" height="136" alt="Scenically Wired" /></a>
You need to strip out everything but the <a tag and the <img tag, so that they have no attributes. Like this:
<a href="http://www.flickr.com/photos/mystic-venus/2874071881/"><img src="http://farm4.static.flickr.com/3059/2874071881_5e05fbb707_m.jpg" /></a>
So the "title" "width" "height" and "alt" attributes have all been stripped.
Sorry I can't change this to make it simple to cut and paste, but that's the way the forum is designed. I might see if the forum can be hacked to allow those attributes, but it's a low priority right now.
I've fixed your post to display your image correctly Chrissy
