PBN1 wrote:
How can you add an image in Mail without being an attachment?
You don't.
It's not possible. The e-mail protocol is designed for text; anything else has to go as an attachment.
Different mail clients (such as Mail.app, the mail client bundled with Mac OS X) may have different ways of handling such attachments, but they are still attachments. Each mail client has its own rules and methods, so one may display a picture as if it were in the body of the message, but another client may do something completely different.
A way of faking it is to format your message in HTML (which is a kind of text). The image is hosted on a remote server, not added to the message; instead, you include a link to it in the body of the message, as you would when building a web page. (This is also what the two tips helpfully provided by X423424X do, except that the link to the image is added in the signature, rather than the body of the message.) What exactly happens to it is, again, at the discretion of the mail client. In my case, for instance, displaying images in HTML messages is turned off, and will stay resolutely off.