gistfile1.txt

<?php
function update_attachment() {
	global $post;
	wp_update_attachment_metadata( $post->ID, $_POST['a_image'] );

	if( !empty( $_FILES['a_image']['name'] )) {
		require_once( ABSPATH . 'wp-admin/includes/file.php' );

		$override['action'] = 'editpost';
		$file = wp_handle_upload( $_FILES['a_image'], $override );

		if ( isset( $file['error'] )) {
			return new WP_Error( 'upload_error', $file['error'] );
		}

		$file_type = wp_check_filetype($_FILES['a_image']['name'], array(
			'jpg|jpeg' => 'image/jpeg',
			'gif' => 'image/gif',
			'png' => 'image/png',
		));
		
		if( $file_type['type'] ) {
		
			$name_parts = pathinfo( $file['file'] );
			$name = $file['filename'];
			$type = $file['type'];
			$title = $_POST['a_title'] ? $_POST['a_title'] : $name;
			$content = $_POST['a_desc'];

			$post_id = $post->ID;
			$attachment = array(
				'post_title' => $title,
				'post_type' => 'attachment',
				'post_content' => $content,
				'post_parent' => $post_id,
				'post_mime_type' => $type,
				'guid' => $file['url'],
			);

			foreach( get_intermediate_image_sizes() as $s ) {
				$sizes[$s] = array( 'width' => '', 'height' => '', 'crop' => true );
				$sizes[$s]['width'] = get_option( "{$s}_size_w" ); // For default sizes set in options
				$sizes[$s]['height'] = get_option( "{$s}_size_h" ); // For default sizes set in options
				$sizes[$s]['crop'] = get_option( "{$s}_crop" ); // For default sizes set in options
			}

			$sizes = apply_filters( 'intermediate_image_sizes_advanced', $sizes );

			foreach( $sizes as $size => $size_data ) {
				$resized = image_make_intermediate_size( $file['file'], $size_data['width'], $size_data['height'], $size_data['crop'] );
				if ( $resized )
					$metadata['sizes'][$size] = $resized;
			}

			$attach_id = wp_insert_attachment( $attachment, $file['file'] /*, $post_id - for post_thumbnails*/);

			if ( !is_wp_error( $id )) {
				$attach_meta = wp_generate_attachment_metadata( $attach_id, $file['file'] );
				wp_update_attachment_metadata( $attach_id, $attach_meta );
			}
			update_post_meta( $post->ID, 'a_image', $images );
		}
	}
}