Index: wp-includes/class-wp-xmlrpc-server.php
===================================================================
--- wp-includes/class-wp-xmlrpc-server.php	(revision 18388)
+++ wp-includes/class-wp-xmlrpc-server.php	(working copy)
@@ -1596,6 +1596,7 @@
 			'caption'				=> $attachment->post_excerpt,
 			'description'			=> $attachment->post_content,
 			'metadata'				=> wp_get_attachment_metadata($attachment->ID),
+			'id'					=> $attachment->ID,
 		);
 
 		return $attachment_struct;
@@ -2157,6 +2158,7 @@
 	 *  - wp_page_parent_id
 	 *  - wp_page_order
 	 *  - wp_author_id
+	 *  - wp_featured_image
 	 *  - post_status | page_status - can be 'draft', 'private', 'publish', or 'pending'
 	 *  - mt_allow_comments - can be 'open' or 'closed'
 	 *  - mt_allow_pings - can be 'open' or 'closed'
@@ -2415,6 +2417,9 @@
 		if ( isset($content_struct['custom_fields']) )
 			$this->set_custom_fields($post_ID, $content_struct['custom_fields']);
 
+		if ( isset($content_struct['wp_featured_image']) && $content_struct['wp_featured_image'] )
+			update_post_meta($post_ID, "_thumbnail_id", $content_struct['wp_featured_image']);
+
 		// Handle enclosures
 		$thisEnclosure = isset($content_struct['enclosure']) ? $content_struct['enclosure'] : null;
 		$this->add_enclosure_if_new($post_ID, $thisEnclosure);
@@ -2728,6 +2733,13 @@
 				unstick_post( $post_ID );
 		}
 
+		if ( isset($content_struct['wp_featured_image']) && $content_struct['wp_featured_image'] ) {
+			update_post_meta($post_ID, "_thumbnail_id", $content_struct['wp_featured_image']);
+		}
+		else {
+			delete_post_meta($post_ID, "_thumbnail_id", "");
+		}
+
 		if ( isset($content_struct['custom_fields']) )
 			$this->set_custom_fields($post_ID, $content_struct['custom_fields']);
 
@@ -2860,6 +2872,14 @@
 
 			if ( !empty($enclosure) ) $resp['enclosure'] = $enclosure;
 
+			foreach ( $resp['custom_fields'] as $custom_field ) {
+				if ( $custom_field["key"] == '_thumbnail_id' ) {
+					if ( $imageurl = wp_get_attachment_url($custom_field['value']) ) {
+						$resp['wp_featured_image'] = array( 'id' => $custom_field['value'], 'url' => $imageurl );
+					}
+				}
+			}
+
 			return $resp;
 		} else {
 			return new IXR_Error(404, __('Sorry, no such post.'));
@@ -2967,6 +2987,15 @@
 				'wp_post_format' => $post_format
 			);
 
+			$entry_index = count($struct) - 1;
+
+			foreach ( $struct[$entry_index]['custom_fields'] as $custom_field ) {
+				if ( $custom_field['key'] == '_thumbnail_id' ) {
+					if ( $imageurl = wp_get_attachment_url($custom_field['value']) ) {
+						$struct[$entry_index]['wp_featured_image'] = array( 'id' => $custom_field['value'], 'url' => $imageurl );
+					}
+				}
+			}
 		}
 
 		$recent_posts = array();