My daughter just showed me how to do this! But, the pictures can't be too large(my daughter resized it for me to 200 X 150 pixels, so if you pic is larger than that I can't help as I don't know how to do that yet.
First step; must be a Registered Member, as only then will you have access to the User CP function.
Use the Post Reply button on the left rather than Quick Reply.
Write you message, then;
Scroll down to Manage Attachments and click;
Click Browse, which brings up your files.
Choose a picture and click on it, then click on Open.
Click Upload, Close Window, then Submit!
Hope it works for you
