You have to have the picutre uploaded to a server that allows hot linking of images.
http://groups.msn.com works.
Just grab the url of the pic that you want to post and press

button and paste the url of the pic in between the (image) and (/image). (they have square brackets)
To get the url (ie http:www.thepic.jpg) you have to right click the image and press properties. Copy and past the url.