You have to upload to a picture hosting site, such as
http://s648.photobucket.com/
or https://www.tumblr.com/
or http://tinypic.com/
or http://www.flickr.com/

Once you've created an account and uploaded your picture, copy the link location, click the add pic button, and paste the link location.
It is better explained here: http://gunownersofcanada.ca/showthre...-Post-Pictures
Hope this helps.