Within the next few weeks, the ROBLOX Games page is undergoing a major overhaul that will make the page cleaner, easier to navigate, and provide space for even more games to be showcased. Part of this page makeover are the new Game Icons that will appear instead of the current thumbnails. Icons are square images that are meant to act more as logos for your games.
Not to worry, ROBLOX is not removing thumbnails. Thumbnail images will continue to exist on the Game Details page (i.e., the page that contains the Play button). Game icons are meant to help developers distinguish their game in a format that can be used for multiple purposes across ROBLOX.