This question already has an answer here:
CiviCRM emails don't display uploaded images to the recipients. I think that the problem is that when I upload the image it sets the image src URL to "site/default/files/..." and doesn't include "http://www.mysite.com". When I go in and manually enter "http://www.mysite.com", everything works.
How do I fix this so that when I upload an image it includes the base URL in the image's src URL?