Index: wp-includes/media.php
===================================================================
--- wp-includes/media.php	(revision 23135)
+++ wp-includes/media.php	(working copy)
@@ -836,8 +836,14 @@
 
 	$k = $prev ? $k - 1 : $k + 1;
 
-	if ( isset($attachments[$k]) )
-		echo wp_get_attachment_link($attachments[$k]->ID, $size, true, false, $text);
+	$output = $attachment_id = null;
+	if ( isset($attachments[$k]) ) {
+		$attachment_id = $attachments[ $k ]->ID;
+		$output = wp_get_attachment_link( $attachment_id, $size, true, false, $text );
+	}
+
+	$adjacent = $prev ? 'previous' : 'next';
+	echo apply_filters( "{$adjacent}_image_link", $output, $attachment_id, $size, $text, $attachments );
 }
 
 /**