HTML5 is all about open standards, I don’t think there is something that will allow to protect your game’s data (images, sounds, etc) or even source code, to an extend (your code could use JS obfuscator to make the process harder to steal your code). For images, maybe you could find a library that encrypts your data, but I am not aware if this even exists for Javascript. As an alternative of putting all your images into only 1 file, using multiple files would already make the process of taking your images more “difficult” at the cost of changing your code and maybe a little slower loading time.