Lucario. Listen, bud. Just listen to me, ignore everyone else. At the bottom of your thread, click "Post". It should be a darker color than the other buttons.
You'll be on a new screen with a lot of different posting options. Ignore everything but the really tiny Mona Lisa picture at the far left of these options, on the second row. It should be right above the "eye rolling" emote. When you click this, you can copy and paste the URL (or link) of the picture into the box.
Click "OK". The picture should pop up in the post box. Then do with it what you will. Easy. Don't worry about using anything but that. It's so easy, a little 5 year old could do it. Literally.
If you still can't get it after my easy instructions, you are either mentally handicapped trolling everyone as Ty.