header image has unwanted edge

I have uploaded a png image with transparent background. When I go to the Appearances > Header and pull it in, the preview shows no edge or border, which is as desired. But when I go to the actual site, there is a faint edge that makes it look sloppy and I cannot discern where that is coming from and therefore how to remedy it. Advice welcome.

https://www.militaryacademiesedge.com