I'm sure there's an easy answer and I feel a little daft for asking, but can anyone tell me how this is done please?

Thanks

You cant do it from mobile. Go on your comouter and it becomes a bit more obvious, it is a small square picture button.

If y o u use something like photobucket tou can add links to your pictures from mobile

_{Thanks guys!}

I use imgur and drop the link it gives me. No account needed.