If you're replying to an existing thread, hit Reply in the post first and then follow the three steps below.
When you're ready to add a pic to your message
See Attachments located above the Message box
Click on
Attach a file... (Make sure your pic is in a valid pic format: gif, jpb, png, jpeg. It can't be larger than 614.4 K

Click on Choose File button (go to the folder and file on your pc where your pic is located. Click on the pic you want to attach and then OPEN. Choose a pic from your Photo Library if you're on an iPhone or take a photo to use)
Click on Attach button in your post
You will see a message in the light gray area above the Message box showing the pic is attached. If you change your mind and don't want to post the pic after you've already attached it, simply hit the Delete button). If there's a different pic you want to add, follow the same steps.
You can attach up to 6 files to a post.