Unconditionally re-encode locally-uploaded images to strip metadata

This strips metadata on file upload by re-encoding the files, at the cost
of possible slight image quality decrease and processing resources.

lib/paperclip/lazy_thumbnail.rb

@@ -20,7 +20,7 @@ module Paperclip
     private
 
     def needs_convert?
-      needs_different_geometry? || needs_different_format?
+      needs_different_geometry? || needs_different_format? || needs_metadata_stripping?
     end
 
     def needs_different_geometry?
@@ -31,5 +31,9 @@ module Paperclip
     def needs_different_format?
       @format.present? && @current_format != @format
     end
+
+    def needs_metadata_stripping?
+      @attachment.instance.respond_to?(:local?) && @attachment.instance.local?
+    end
   end
 end