Campbell...when you post a reply...you will see a box next to the submit block that says Attach files or Add files or something like that. Click on that...you will see a bar with a button next to it that says browse.
If you have the picture on your computer..."browse" to where it is and then click on the picture..the open button and then ok. When you are done..click Submit on your post...DO NOT CLICK ON PREVIEW. Then your pic will be added.