From looking up the first butterfly in the course, it looks like the two images shown are the upside and downside of the butterfly, respectively (from left to right). Is that right? Also, is the butterfly shown always a male specimen? (To be honest I don’t even really know how much of a difference sex makes in terms of butterfly appearance.)
The female is often different from the male so ideally they should be shown as and the underside is different to the top (but usually considerably different), so it is helpful if it distinguishes, but often (in my books) it is the male then the female.
When the underside is shown, it is usually shown on the same butterfly. The top side is shown on the left attached to the abdomen but the underside (half) wing shown on the right separated by a small gap.
@VincentOostelbos I think you are correct. The left image is the upperwing while the right hand image shows the underwing. In those specimens of butterfly where males and females differ, for example the Orange Tip in level 1, only the male butterfly has been shown.