here's my case for Legit:
1. They remembered the masks. They appear on every cover.
2. The scene depicted fits with Milton's work. (for the slow, that would be Paradise Lost the book.)
3. It's kinda CGI in a cheesy amateurish way. No offense, but SX covers tend to look that way (except The Odyssey).
4. It seems too detailed to be a joke/fake cover. If it is indeed a fake cover, the artist is familiar with Paradise Lost's themes and characters and is also familiar with the SX cover style (see above 3.), font, and put enough time and effort into it to be taken seriously.
Hence, I conclude it's either real or a very good fake. Also, as a footnote:
5. It was posted on BW. BW tends to be 1000 times more reliable than the ever-idiotic blabbermouth.