gistfile1.php

<?php
/*
How To Locally Mirror Remote Images With WordPress
*/


// URL of the image you want to mirror. Girl in pink underwear for instance.
$image = 'http://i.imgur.com/Hq4QA.jpg';

// GET request
$get = wp_remote_get( $image );

// Check content-type (eg image/png), might want to test & exit if applicable
$type = wp_remote_retrieve_header( $get, 'content-type' );

// Mirror this image in your upload dir
$mirror = wp_upload_bits( basename( $image ), '', wp_remote_retrieve_body( $get ) );

/* Sample output for mirror:
array(3) {
  ["file"]=>
  string(64) "E:\home\planetozh\wordpress/wp-content/uploads/2010/09/Hq4QA.jpg"
  ["url"]=>
  string(63) "http://127.0.0.1/wordpress/wp-content/uploads/2010/09/Hq4QA.jpg"
  ["error"]=>
  bool(false)
}
*/

// Attachment options
$attachment = array(
    'post_title'=> basename( $image ),
    'post_mime_type' => $type
);

// Add the image to your media library (won't be attached to a post)
wp_insert_attachment( $attachment, $mirror['file'] );