The first step to posting a picture is to get the URL address of the picture you want to post. If the picture is already on the Internet, locate it and then click on it using the right mouse button. Then click on "Properties." This will bring up a box. Find the "Address" line. If this line is a URL address and contains the word "images" or "photos" or something similar, cut and paste it.
If the picture you want to post is not on the Internet, you need to create a URL address for it by posting on a site like Photobucket [http://www.photobucket.com/].
Once you have the URL address, start a new post and then click on the button that has an image of a tree on it. A little box will pop up. Fill in at minimum the "Image URL" line. You can fill in the other fields if you want. Click "Insert" and you're done!