How do you post the picture from one's desktop on a computer ?
You have to post it to a website or server that has html links. For example, find the picture on any website on the internet, right click on the picture, click properties, tripple click on the Http://wxyz.jpg part and then hit control-c to copy the link.
Write your (img src=" hit control-x to paste your link, then finish with ")
remember to use >'s instead of )'s.
There you go, use preview to make sure it is all correct, if it is you will get the picture in your post, if not you will get a small white box with a red x.
Good luck!