Index: src/wp-includes/pluggable.php
===================================================================
--- src/wp-includes/pluggable.php	(revision 29650)
+++ src/wp-includes/pluggable.php	(working copy)
@@ -2200,6 +2200,28 @@
 }
 endif;
 
+if ( !function_exists( 'get_avatar_url' ) ) :
+/**
+ * Retrieve the avatar url for a user who provided a user ID or email address.
+ *
+ * @uses get_avatar() Retrieves img tag string for user's avatar.
+ *
+ * @param int|string|object $id_or_email A user ID,  email address, or comment object
+ * @return string Empty string url not found or avatar URL.
+*/
+function get_avatar_url( $id_or_email ) {
+	$avatar_html = get_avatar( $id_or_email );
+
+	preg_match( '/src=["|\'](.+)[\&|"|\']/U', $avatar_html, $matches );
+
+	if ( ! empty( $matches[1] ) ) {
+		return esc_url_raw( $matches[1] );
+	}
+
+	return '';
+}
+endif;
+
 if ( !function_exists( 'wp_text_diff' ) ) :
 /**
  * Displays a human readable HTML representation of the difference between two strings.