PMXI_GALLERY_IMAGE

/**
 * @param $post_id int    - The id of the post just created/updated
 * @param $att_id  int    - The attachment id of the image
 * @param $file    string - The local file path to the full size image
 */
function my_gallery_image( $post_id, $att_id, $file ) {


}

add_action( 'pmxi_gallery_image', 'my_gallery_image', 10, 3 );
LL Cool Trey