Butterflies - spot the difference

I wonder how many times I spot a butterfly or insect and think I already have a picture of it only to find that it is in fact different to what I have??
The two pictures below are a good example of this and how careful I have to be. See if you think they are the same......

Both these belong to the Pieridae family, genesus Mylothris. The one above is a Twin Dotted Border (Mylothris rueppellii haemus) and the one below a Common Dotted Border (Mylothoris agathina)

The difference being the two dots on the top of the wings. The top picture is the underside of the female Twin Dotted and the picture below is the underside of the male Common Dotted.