This hook allows images inserted to replace the {IMAGE} keyword to be resized. Default WordPress sizes can be used to physical sizes can be passed in an array.
function my_s2_image_size() { // return a pre-defined size like 'thumbnail' or 'full' // or return a physical size as an array like array(300, 300) or array(150, 150)
// examples: return 'thumbnail'; return 'full'; return array(300,300);}add_filter('s2_image_size', 'my_s2_image_size');