When you click the paper clip icon, it'll pull up the manage attachments box. All you need to do is click browse, find the picture, then click upload. Once it uploads, just close the box out, then submit your message.
"What, exactly, is the internet? Basically it is a global network exchanging digitized data in such a way that any computer, anywhere, that is equipped with a device called a 'modem', can make a noise like a duck choking on a kazoo." - Dave Barry