When you start a new topic or reply to a topic, right under the text box to enter your reply and above the "post" button, there is a link that reads "Additional Options". Click on it and it will slide down a box to attach a photo.
When you post, look below the area where you type and you will see "additional options" . Click on that and you will see "Attach:" followed by and empty box and "Browse..." Click on Browse and select the image from your saved files and that is how you post. Some images can be too large and if that is the case for you look at the top of the message boards here and Jason has a post to help with that. Best of luck