If you have a photo of yourself uploaded to the web, just add the location (which will be http://
something ) into your profile, in the bit called "Picture URL". If you haven't put a photo of yourself onto the web, you can visit a site like photobucket to put one there.
http://photobucket.com/The biggest confusion people have is understanding that your photo needs to be uploaded for it to be seen on websites like CBF. A photo on your hard drive cannot be used, it has to be uploaded to a website. For everyday use, photobucket will take your photo and it will be uploaded and useable here and on other sites.