are you copying the link for the page or for the image? it needs to be the image link (left click with the mouse, "copy link from image"). If it still doesn't work, it might be bc the site is not compatible. in this case, I advise you to save the image and upload it into another site, like tumblr or imgur, and then copy the image link (my banner and pfp are both uploaded in a private tumblr blog, for example).