Index: wp-admin/includes/media.php
===================================================================
--- wp-admin/includes/media.php	(revision 19186)
+++ wp-admin/includes/media.php	(working copy)
@@ -766,12 +766,15 @@
 	elseif ( $url_type == 'post' )
 		$url = $link;
 
-	return "
-	<input type='text' class='text urlfield' name='attachments[$post->ID][url]' value='" . esc_attr($url) . "' /><br />
-	<button type='button' class='button urlnone' title=''>" . __('None') . "</button>
-	<button type='button' class='button urlfile' title='" . esc_attr($file) . "'>" . __('File URL') . "</button>
-	<button type='button' class='button urlpost' title='" . esc_attr($link) . "'>" . __('Post URL') . "</button>
-";
+	$output = "
+		<input type='text' class='text urlfield' name='attachments[$post->ID][url]' value='" . esc_attr($url) . "' /><br />
+		<button type='button' class='button urlnone' title=''>" . __('None') . "</button>
+		<button type='button' class='button urlfile' title='" . esc_attr($file) . "'>" . __('File URL') . "</button>
+		<button type='button' class='button urlpost' title='" . esc_attr($link) . "'>" . __('Post URL') . "</button>
+	";
+
+	return apply_filters( 'image_link_input_fields_output', $output, $post, $url_type, $file, $link );
+
 }
 
 /**