Shortcode to link image to single post

<?php
// http://www.gravityhelp.com/forums/topic/link-uploaded-image-to-created-post#post-76548
// http://wordpress.stackexchange.com/a/44069
// Chris Hajer 17 November 2012
add_shortcode('gf_postimage', 'get_image_with_link');
function get_image_with_link() {
        global $post;
        $all_images = get_posts( array(
                // Return just the first attachment
                'numberposts' => 1,
                'order'=> 'ASC',
                'post_parent' => $post->ID,
                'post_mime_type' => 'image',
                'post_type' => 'attachment'
        ) );
        // Step through all image attachments
        foreach ( $all_images as $image ) {
                // Get the attachment ID
                $image_id = $image->ID;
                // Get the image alt tag
                $image_alt = get_post_meta($image_id, '_wp_attachment_image_alt', true);
                // Get the attachment URL for the large size
                $image_info = wp_get_attachment_image_src( $image_id, 'large' );
                // Get the parent post ID
                $parent_id = $image->post_parent;
                // Get the parent post Title
                $parent_title = get_the_title( $parent_id );
                // Get the parent post permalink
                $parent_permalink = get_permalink( $parent_id );
        }
        $post_content_prepend = "<a href='$parent_permalink' title='$parent_title'><img src='{$image_info[0]}' width='{$image_info[1]}' height='{$image_info[2]}' alt='$image_alt' class='size-large alignnone wp-image-$image_id'  /></a>";
        return $post_content_prepend;
}