Avoid posting large pictures. It is best to keep them not more than 500 pixels wide. That way the dial-up folks aren't bogged-down, and the width doesn't make the page hard to read in a standard sized window.
This forum does not host your images. You need to have a place like Flickr, Snapfish, Photobucket, etc., or your own site.
To insert an image, click the first icon in the row just above the smiley faces when you are composing a message. Then just type the URL of your image between the two tags.