If it is an image that you have on your computer and have used the Paper Clip icon to attach it, you will need to scroll over to the far right of the screen to click on the Upload button. If it is a link, you can click on the address bar until the whole address is highlighted and copy that, then past in the reply.
Or additional info as a description, or person's name or how you found it - pinterest or images or ???
Janey - Neat people never make the exciting discoveries I do.