I hope this isn't a completely redundant post because I hate repetitive post on forums; however, I searched the forums, wiki, tutorials, and search engines and have not found an answer to my problem.

I have a large logo image (1683px × 1282px) that I need to scale down to size for the page. It is obviously way too big, and I need to shrink it down to size. The logo I am talking about is the logo in the header section. I realize I can do this in photoshop, but the tutorials and my experience in web development tells me that I should be able to do this in the php. All of the info that I have found on this subject tell me to edit header.php and save it in the custom directory, which I have done. Essentially, the image works and displays; however, it does not scale down to the specified width and height.

If you need to see what I am talking about here is the store site, it is my first venture into zen cart and I just started working on it.
http://www.woodvilleusa.com/store/

Here are my settings in header.php:

// added defines for header alt and text
define('HEADER_ALT_TEXT', 'Woodville USA');
define('HEADER_SALES_TEXT', '');
define('HEADER_LOGO_WIDTH', '841px');
define('HEADER_LOGO_HEIGHT', '641px');
define('HEADER_LOGO_IMAGE', 'logo.jpg');


Thank you for your time.