Hi, I would get rid of the background, then convert image to greyscale and adjust the contrast, then either:
Image> adjustments> Posterize> 2 (you may have to go back and play with the contrast to get it like the Che image)
or Filter> Stamp and play around with the sliders, then clean up any random bits with the eraser tool make the solid black and white chunks.
Sorry this is a bit rushed, my 2 year old daughter wants me to play with her.