Daragh, When you write a message you have all those buttons across the window you type in, right? Where you can bold font etc. The rightmost button is for inserting images.
All you need is the URL of an image (that ends with *.jpg or *.gif) and it will show up in the message.
So, using the image button, "http://www.shakenstir.co.uk/siteassets/damo4.jpg" turns into
