It is quite easy to post an image, put you need to host it on another website and to paste the url link.
http://www.imageshack.us/
It is a website where you can host picture.

You just have to Find the picture and then click on "Host it"
Then you have to copy and paste the "direct link to image"
and then you have to click on "image"


If you have any question about the image ask here

other tip : once you have the link for your picture, you can also insert it that way :

Code:

[img]http://www.mylink.com/huhu.jpg[/img]