drop a blank index.html file into that folder before uploading to server. Or add the line <p>Images folder moved to aws</p> inside html file.
But if they want to get images they will and very easily by pressing F12 and saving them all along with all your code. THey can download your whole game and host it elsewhere too.
Downside of html5 games. But they can steal any game on the planet, no matter how much security the game developers put in. So don't worry about it - they will steal it, but how you incorp that into your marketing plan is up to you.