[Theme: Tremor] Trouble with header pic

In the header.php and style.css files, it says “upload a file named header.png to the theme image file.” I have placed this file in both tremor/images and in the images file of the root of the site, and still the header pic is not appearing. I’m wondering if the header.png needs to be a specific size or anything; this is not indicated, and there isn’t a “custom header” option under Appearance. Any help appreciated.

http://wordpress.org/extend/themes/tremor/