well i look and i look and finally i found this work that work for me.
$upload = wp_upload_bits( $_FILES['image']['name'], null, file_get_contents( $_FILES['image']['tmp_name'] ) );
$wp_filetype = wp_check_filetype( basename( $upload['file'] ), null );
$wp_upload_dir = wp_upload_dir();
$attachment = array(
'guid' => $wp_upload_dir['baseurl'] . _wp_relative_upload_path( $upload['file'] ),
'post_mime_type' => $wp_filetype['type'],
'post_title' => preg_replace('/\.[^.]+$/', '', basename( $upload['file'] )),
'post_content' => '',
'post_status' => 'inherit'
);
$attach_id = wp_insert_attachment( $attachment, $upload['file'], $post_id );
require_once(ABSPATH . 'wp-admin/includes/image.php');
$attach_data = wp_generate_attachment_metadata( $attach_id, $upload['file'] );
wp_update_attachment_metadata( $attach_id, $attach_data );
update_post_meta( $post_id, '_thumbnail_id', $attach_id );
wp_redirect( site_url() . '/thank-you/' );
die();
}
from here