Yep, I think blurring will be your best & easiest option. The only thing to think about is how much blur to add, not enough and stepping will still be apparent, too much and other detail will be lost. My suggestion would be to make several copies and blur them to different degrees from barely noticable to quite severe, and see which works best. It will depend on the original's resolution as well. BTW, where did you get the image?