Underneath the text box (you type your message in) you will find the line: "attach an image" and "browse", click on 'browse' and it will take you to your photos. Choose the photo you would like to upload and click on it. You can upload one photo per message (but all in the same thread). Just make sure your photos aren't exceeding the 500 pixels. If so, do make sure to resize them before starting this process
