To send it in the body, the email has to be sent as html (like this webpage) and the image itself ISN'T in the email, but a link to the image is. If you send an email with a 5MB image in it then the email itself will not be 5MB as the image is saved on a server online just like every other image/html page is that's used in webpages. Geddit? You're effectively sending a webpage, not just a simple email.
To link to an image you'll either have to upload it and save it's full location, or note the location of an existing online image (although there are obvious copyright issues here!), e.g.
http://freestockphotos.com/SCENERY1/AlpineRMNP.jpeg
I'd have a look at an html tutorial as I'm sure I'm explaining this badly but the code you need to type to include this pic would be:
<img src="http://freestockphotos.com/SCENERY1/AlpineRMNP.jpeg" width="576" height="386" alt="nice scenic picture, property of freeStockPhotos.com" />
I hope this works...