If you are using Windows Live Mail, then to send pictures, you need to register your ID. If you look along the top, left to right, you should see a box that says something about ID?
I'm sorry, I can't remember what ID I had to use. I actually rarely use WLM, only if I want to send pictures to a particular friend. I remember having to do this before I could email pictures.
Hopefully, just doing that will rectify this issue for you.