Source

File: wp-includes/deprecated.php

function get_attachment_icon_src( $id = 0, $fullsize = false ) {
	_deprecated_function( __FUNCTION__, '2.5.0', 'wp_get_attachment_image_src()' );
	$id = (int) $id;
	if ( !$post = get_post($id) )
		return false;

	$file = get_attached_file( $post->ID );

	if ( !$fullsize && $src = wp_get_attachment_thumb_url( $post->ID ) ) {
		// We have a thumbnail desired, specified and existing.

		$src_file = wp_basename($src);
	} elseif ( wp_attachment_is_image( $post->ID ) ) {
		// We have an image without a thumbnail.

		$src = wp_get_attachment_url( $post->ID );
		$src_file = & $file;
	} elseif ( $src = wp_mime_type_icon( $post->ID ) ) {
		// No thumb, no image. We'll look for a mime-related icon instead.

		$icon_dir = apply_filters( 'icon_dir', get_template_directory() . '/images' );
		$src_file = $icon_dir . '/' . wp_basename($src);
	}

	if ( !isset($src) || !$src )
		return false;

	return array($src, $src_file);
}