First thing to remember is that you can't upload a picture from your PC, but you can post a link to a picture already stored somewhere on the net.

To post a picture, right-click on the picture and select "copy image location" (Netscape, see below for Explorer), then paste it into the "picture URL" box of the message.

For Explorer, you must first right-click on the picture and select "Properties".   From the Properties window, highlight the URL address and copy the link with Ctrl+C.  Firefox is easier, when you right click on a picture, you have the option to copy the image location.  Once you copied the location, paste it into the "picture URL" box of the message, include the http:// prefix.

For example, this URL address:
http://www.theeroticreview.com/images/image_escort_reviews.gif
will display the picture below, when added to the 'picture URL' box on the 'POST A MESSAGE' or 'POST REPLY' screen.  If the file format is one that TER supports (I think this is only gif and jpg) your picture will appear below your message. Like this: