Hook after attachment added and cropped

There is to filters needed for optimizing all images, that will be uploaded:

add_filter('wp_handle_upload', 'random_function', 10, 2);
add_filter('image_make_intermediate_size', 'rand_function2', 10, 1);

function random_function($array, $string) {
// Some random action with main image
return $array
}

function rand_function2($file) {
// Some random action with cropped images
return $file
}