When you use the WP_CONTENT_URL constant you are telling WordPress that image/media files are stored on the static subdomain so you would not need any sort of additional .htaccess redirect code. I noticed that you had https instead of just http. That could have been the problem. You would not need to add a plugins define constant when setting a cookie domain.
define('COOKIE_DOMAIN', 'www.opnutrition.com'); define('WP_CONTENT_URL', 'http://static.opnutrition.com/wp-content');
All media files are uploaded and stored on the static.opnutrition.com website and the WP_CONTENT_URL constant in your main site’s wp-config.php file will use that URL for where to look for those media files. Your image URL’s on your main site will point to the static subdomain. Cookies will not be included in the Request.