WordPress/wp-admin/media-upload.php

<?php
/**
 * Manage media uploaded file.
 *
 * There are many filters in here for media. Plugins can extend functionality
 * by hooking into the filters.
 *
 * @package WordPress
 * @subpackage Administration
 */

if ( ! isset( $_GET['inline'] ) )
	define( 'IFRAME_REQUEST' , true );

/** Load WordPress Administration Bootstrap */
require_once( dirname( __FILE__ ) . '/admin.php' );

if (!current_user_can('upload_files'))
	wp_die(__('You do not have permission to upload files.'));

wp_enqueue_script('plupload-handlers');
wp_enqueue_script('image-edit');
wp_enqueue_script('set-post-thumbnail' );
wp_enqueue_style('imgareaselect');
wp_enqueue_script( 'media-gallery' );

@header('Content-Type: ' . get_option('html_type') . '; charset=' . get_option('blog_charset'));

// IDs should be integers
$ID = isset($ID) ? (int) $ID : 0;
$post_id = isset($post_id)? (int) $post_id : 0;

// Require an ID for the edit screen
if ( isset($action) && $action == 'edit' && !$ID )
	wp_die( __( 'Cheatin&#8217; uh?' ) );

	if ( ! empty( $_REQUEST['post_id'] ) && ! current_user_can( 'edit_post' , $_REQUEST['post_id'] ) )
		wp_die( __( 'Cheatin&#8217; uh?' ) );

	// upload type: image, video, file, ..?
	if ( isset($_GET['type']) )
		$type = strval($_GET['type']);
	else
		$type = apply_filters('media_upload_default_type', 'file');

	// tab: gallery, library, or type-specific
	if ( isset($_GET['tab']) ) {
		$tab = strval($_GET['tab']);
	} else {
		/**
		 * Filter the default tab in the legacy (pre-3.5.0) media popup.
		 *
		 * @since 2.5.0
		 *
		 * @param string $type The default media popup tab.
		 */
		$tab = apply_filters( 'media_upload_default_tab', 'type' );
	}

	$body_id = 'media-upload';

	// let the action code decide how to handle the request
	if ( $tab == 'type' || $tab == 'type_url' || ! array_key_exists( $tab , media_upload_tabs() ) )
		do_action("media_upload_$type");
	else
		do_action("media_upload_$tab");