Can I add a picture to a message which I have on my computer but isn't on the internet? Can I add a picture to a message which I have on my computer but isn't on the internet?
Kind of. You can make your computer a webserver. It would technically be on the internet, but the image would stay on your computer.
I don't recommend it in most cases. A shared house I used to live in had a little website hosted on one of our PCs, but it would only be accessable as long as the computer was turned on. Also - it opens you up to very real issues of security.
As above, its a lot easier and safer to upload it to an image hoster, or find someone with their own webspace to host it for you, or get your own webspace.