Adding a photo from your computer:
when you are ready to attach your image:
In the reply to thread message box (or post new thread message box if you are starting a new one)
click on the attachment icon, (the paperclip on the top row of buttons) ringed here
this will open the "manage attachments" window;
click on the browse button which will in turn open the 'choose file' window on your PC. (not shown here)
browse to the picture file on your computer and select it.
its location on your computer will appear in the appropriate
place on the manage attachments window.
click the top "Upload" button
In a few seconds the details of the image should appear in the manage attachments window if the upload was successful as "Current Attachments" (arrowed in the picture)
unless you want to add another image (just repeat the same steps), that's it.
Close the manage attachments window and carry on writing your message - or submit the message if you were finished anyway.
(note: you wont see any reference to the image in the actual message field until you submit it)