--- algorithm.hpp	2012-07-02 18:52:43.222999455 +0900
+++ algorithm.patched.hpp	2012-07-06 06:08:58.127549626 +0900
@@ -735,8 +735,8 @@
         return std::for_each(img.begin().x(), img.end().x(), fun);
     } else {
         for (std::ptrdiff_t y=0; y<img.height(); ++y)
-            fun = std::for_each(img.row_begin(y),img.row_end(y),fun);
-        return fun;
+            std::for_each(img.row_begin(y),img.row_end(y),fun);
+        return std::move(fun);
     }
 }