White border around header background image on frontpage.

Dear,

With some images i use for a background header image on my frontpage, i get a nasty looking white border around it. It’s not with all images, but with the best looking this happens. I know have an image on it which has this issue (on gnes.emclogics.com).

Is there anyone whom can help me with this to solve it? I tried padding the image, giving it a border, repositioning, cutting edges, and more, but no success.