If your photos are hosted on another site (such as your personal Web site, Flickr account, or something similar), click the Image icon in the toolbar above the message box (it looks like a brown picture frame with a landscape scene in it). Then copy and paste the photo URL into the pop-up window and click OK.
To browse your computer for photo files, click the Attach Files button beneath the message box. An Attachments window will appear. Click Choose File, navigate to your photo, click Choose, and your photo name will appear in the Attachments window. Repeat the process to add more photos, and when you're finished, click Save to post your message.