When you bring up the box to type a new topic or hit reply on a topic below the text box you will see FILE ATTACHMENTS. Click on choose file, it will bring down a menu to select where your pic is. Go to the pic and select it and it should show under your text. There is a text area next to each one where you can put a title or details. You can put up to 3 pics. Then hit send. DO NOT hit preview or your pics will disappear. I am also on a Mac.