Are you trying to program something? You do realize this is the server support section, right?
And if you want to implement it into something like IPBoard, have fun. You'll have to dwindle with how the site accesses the database by adding their minecraft username, then change the layouts of posts to add the image. Each post would then call a PHP method to return the string for their minecraft name according to their account, which in turn would be used in an image tag in HTML.
To do this, you must know: SQL, HTML / CSS, and PHP.
If you don't know all of the above, don't bother. You didn't really format your question really well, and it's in the wrong section, so I doubt you would.