To add an image to message board, first the image has to be hosted on a web site - you cannot just "upload " the image on this message board. I am using a picture of a McD glass that is on the pgca web site. I right clicked on that picture (BEFORE I went to the message board), selected COPY IMAGE LOCATION, then when entering a message on the message board clicked on the image box under the box where you enter text, and when the Optional Image URL: box comes up I again did a right click and selected Paste to paste the URL into that box and then clicked on Add. You could also just type in the URL of the image that want to include in your message.
I made sure I first removed the "http://" at the beginning of the Optional Image URL box, as my image URL that I copied already had the "http://" in there - I did not want the "http://" in there twice.
It always seems to work for me better if I put in the image first and then type the text.
Note that for the URL that you put in the "Optional Image URL:" box that it must be a jpg or gif or image file - it cannot be an actual web page that ends in "html" or "htm" - that won't work.
When you are done you should click on Preview to see if you have the thing correct and if so your image along with your text should show up OK and then you can click on Post.