Take a look at your original post.
You figured out how to add the IMG tool, but inbetween where your attempt says URL you have to put the web location where your picture is in here. It has to exist on a website somewhere else. You can't upload it to this site, or just have it exist on your computer.
Also look at your 2nd post and see how I modified the website so that people could just click on it.
Note- I told the user I was modifying the post so he could easily see how it was done by using the modify function.