Index: wp-admin/includes/media.php
===================================================================
--- wp-admin/includes/media.php	(revision 21224)
+++ wp-admin/includes/media.php	(working copy)
@@ -777,13 +777,18 @@
 		$url = $file;
 	elseif ( $url_type == 'post' )
 		$url = $link;
-
-	return "
-	<input type='text' class='text urlfield' name='attachments[$post->ID][url]' value='" . esc_attr($url) . "' /><br />
-	<button type='button' class='button urlnone' data-link-url=''>" . __('None') . "</button>
-	<button type='button' class='button urlfile' data-link-url='" . esc_attr($file) . "'>" . __('File URL') . "</button>
-	<button type='button' class='button urlpost' data-link-url='" . esc_attr($link) . "'>" . __('Attachment Post URL') . "</button>
-";
+	
+	$link_buttons = array(
+		'none' => "<button type='button' class='button urlnone' data-link-url=''>" . __('None') . "</button>",
+		'file' => "<button type='button' class='button urlfile' data-link-url='" . esc_attr($file) . "'>" . __('File URL') . "</button>",
+		'post' => "<button type='button' class='button urlpost' data-link-url='" . esc_attr($link) . "'>" . __('Attachment Post URL') . "</button>"
+	);
+	
+	$link_buttons = apply_filters( 'image_link_buttons', $link_buttons, $post, $url_type, $file, $link );
+	
+	$output = "<input type='text' class='text urlfield' name='attachments[$post->ID][url]' value='" . esc_attr($url) . "' /><br />" . implode( '', $link_buttons );
+	
+	return $output;
 }
 
 function wp_caption_input_textarea($edit_post) {