WordPress: Auto-replace uploaded image with large image size thumbnail

autoreplace-uploaded-wp-image.php

<?php 
/**
 * @author @david
 * replace the WordPress "large" image with the uploaded image
 * put this in your Wordpress functions.php file:
 */
function replace_uploaded_image($image_data) {
// if there is no large image : return
	if (!isset($image_data['sizes']['large'])) return $image_data;

// paths to the uploaded image and the large image
	$upload_dir = wp_upload_dir();
	$uploaded_image_location = $upload_dir['basedir'] . '/' .$image_data['file'];
// $large_image_location = $upload_dir['path'] . '/'.$image_data['sizes']['large']['file']; // ** This only works for new image uploads - fixed for older images below.
	$large_image_location = $upload_dir['basedir'] . '/'.$image_data['sizes']['large']['path'];

// delete the uploaded image
	unlink($uploaded_image_location);

// rename the large image
	rename($large_image_location,$uploaded_image_location);

// update image metadata and return them
	$image_data['width'] = $image_data['sizes']['large']['width'];
	$image_data['height'] = $image_data['sizes']['large']['height'];
	unset($image_data['sizes']['large']);

	return $image_data;
}
add_filter('wp_generate_attachment_metadata','replace_uploaded_image');