The image is reportedly part of promotional artwork for the Chinese market, and shows Mercy wearing a distinctly Grecian outfit. This would of course fit in neatly with the Olympics theme, and would be a neat way of Blizzard resetting the event after last year's Rio Games-inspired celebration.
Here's the image so you can judge for yourself:
This year's Summer Games 2017 is due to begin a little later on today, and will add the usual array of cosmetic items to the game, and also herald the return of Lucioball! Check out our Summer Games guide for a complete breakdown of everything we're expecting to see when the event goes live.