<?php
/*
 * Include the URLs for all image sizes in the WordPress Media Library.
 * Not normally needed but if you're trying to gather a bunch of URLs it helps.
 * Hide the column in Screen Options when not needed.
 *
 * Drop this in your site plugin or function.php
 */

// Adds a "Sizes" column
function sizes_column( $cols ) {
	$cols["sizes"] = "Sizes";
	return $cols;
}

// Fill the Sizes column
function sizes_value( $column_name, $id ) {
	if ( $column_name == "sizes" ) {

		// Including the direcory makes the list much longer but required if you use /year/month for uploads
		$up_load_dir =  wp_upload_dir();
		$dir = $up_load_dir['url'];

		// Get the info for each media item
		$meta = wp_get_attachment_metadata($id);

		// and loop + output
		foreach ( $meta['sizes'] as $name=>$info) {
			echo "<strong>" . $name . "</strong><br>";
			echo "<small>" . $dir . "/" . $info['file'] . " </small><br>";
		}
	}
}

// Hook actions to admin_init
function hook_new_media_columns() {
	add_filter( 'manage_media_columns', 'sizes_column' );
	add_action( 'manage_media_custom_column', 'sizes_value', 10, 2 );
}
add_action( 'admin_init', 'hook_new_media_columns' );