Wordpress - Programmatically adding images to media library

$image_url = 'adress img';

$upload_dir = wp_upload_dir();

$image_data = file_get_contents( $image_url );

$filename = basename( $image_url );

if ( wp_mkdir_p( $upload_dir['path'] ) ) {
  $file = $upload_dir['path'] . '/' . $filename;
}
else {
  $file = $upload_dir['basedir'] . '/' . $filename;
}

file_put_contents( $file, $image_data );

$wp_filetype = wp_check_filetype( $filename, null );

$attachment = array(
  'post_mime_type' => $wp_filetype['type'],
  'post_title' => sanitize_file_name( $filename ),
  'post_content' => '',
  'post_status' => 'inherit'
);

$attach_id = wp_insert_attachment( $attachment, $file );
require_once( ABSPATH . 'wp-admin/includes/image.php' );
$attach_data = wp_generate_attachment_metadata( $attach_id, $file );
wp_update_attachment_metadata( $attach_id, $attach_data );

I had issues with @TrubinE's solution where image files were not getting loaded.

Here is a complete example that worked for me: https://gist.github.com/m1r0/f22d5237ee93bcccb0d9

This is a similar idea but use the WP HTTP library to fetch the content versus file_get_contents(). Here is the content of the github gist solution from m1r0:

        if( !class_exists( 'WP_Http' ) )
        include_once( ABSPATH . WPINC . '/class-http.php' );
    $http = new WP_Http();
    $response = $http->request( $meta[ 'image_url' ] );
    if( $response['response']['code'] != 200 ) {
        return false;
    }
    $upload = wp_upload_bits( basename($meta[ 'image_url' ]), null, $response['body'] );
    if( !empty( $upload['error'] ) ) {
        return false;
    }
    $file_path = $upload['file'];
    $file_name = basename( $file_path );
    $file_type = wp_check_filetype( $file_name, null );
    $attachment_title = sanitize_file_name( pathinfo( $file_name, PATHINFO_FILENAME ) );
    $wp_upload_dir = wp_upload_dir();

    $post_info = array(
        'guid'           => $wp_upload_dir['url'] . '/' . $file_name,
        'post_mime_type' => $file_type['type'],
        'post_title'     => $attachment_title,
        'post_content'   => '',
        'post_status'    => 'inherit',
    );

    $attach_id = wp_insert_attachment( $post_info, $file_path, $parent_post_id );
    require_once( ABSPATH . 'wp-admin/includes/image.php' );
    $attach_data = wp_generate_attachment_metadata( $attach_id, $file_path );
    wp_update_attachment_metadata( $attach_id,  $attach_data );
    return $attach_id; code here

If you use WordPress' sideload feature, you can do this more easily (and have WordPress handle all of the sanitization for you).

<?php
$desc = 'some description';
$file = 'http://www.example.com/image.png';
$file_array  = [ 'name' => wp_basename( $file ), 'tmp_name' => download_url( $file ) ];

// If error storing temporarily, return the error.
if ( is_wp_error( $file_array['tmp_name'] ) ) {
    return $file_array['tmp_name'];
}

// Do the validation and storage stuff.
$id = media_handle_sideload( $file_array, 0, $desc );

// If error storing permanently, unlink.
if ( is_wp_error( $id ) ) {
    @unlink( $file_array['tmp_name'] );
    return $id;
}