When you're posting a reply, hit the button that says "Img" above where you are typing. Then paste the URL address to your picture and hit the "Img" button again (there should be a star in the "Img" box which will go away after you've hit it the second time.) That should work. If you need any more directions just let me know.
Theres a button on my keyboard called "print screen/syRq"... just press it and then go into paint and click paste and the whole sceen should paste and the you can cut. Atleast thats how I do it...I don't know about anyone else though.