Black Border Around Image on Email Campaign Editor

Black Border Around Image on Email Campaign Editor

I have a header image for my email campaign.  It has a transparent background and no border.  When I place the image in the template editor, there is no border.  I have selected the image and clicked "No Border."  When I save the template and send the email, there is a black border around the header image.

How do I fix this?

THanks!