header image code twenty ten

<?php
                    // Check if this is a post or page, if it has a thumbnail, and if it's a big one
                    if ( is_singular() && current_theme_supports( 'post-thumbnails' ) &&
                            has_post_thumbnail( $post->ID ) &&
                            ( /* $src, $width, $height */ $image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), 'post-thumbnail' ) ) &&
                            $image[1] >= HEADER_IMAGE_WIDTH ) :
                        // Houston, we have a new header image!
                        echo get_the_post_thumbnail( $post->ID );
                    elseif ( get_header_image() ) : ?>
                        <img src="<?php header_image(); ?>" width="<?php echo HEADER_IMAGE_WIDTH; ?>" height="<?php echo HEADER_IMAGE_HEIGHT; ?>" alt="" />
                    <?php endif; ?>