Go to your gallery, right click on your picture, and go down to "properties." Click on it, and it will pop up a window. There is a bunch of information about your picture there. At the top of the info, you'll see a web address, starting with
http://yadda yadda. Highlight ALL of that web address, right click and copy.
Now go to your posting window and up at the top of the window you'll see your editing tools. There is a yellow box with a mountain and a sun in it. Click that, and paste into the popup window. Click ok. Your image should show up when you submit the post.