Whenever you click on REPLY to reply to a post, just below the body of your post on the left side there's an icon that says ADDITIONAL OPTIONS. Click on that and the options list opens up, click on the BROWSE icon, which will either open up your computer or your picture files. Just scan through your cache of pictures till you find the one you want to attach, click on ok(?), then click attach and you're done. Just make sure it's small enough to post, or you'll get the error message.
