It does indeed show a Japanese soldier, as Pinterest user Thibaud Danton, has stated on his page: HERE
If you look at the slightly out of focus image, it shows a large, muscular Chinese man (look at the clothing and the hat!) punching a punt, buck-toothed, bespectacled Japanese soldier (complete with katana sword on the side), with the message for the Japanese to get out of China and her territories.
Geez… did EVERYONE use that caricature of the Japanese in their propaganda? Seems like it!
It's interesting to me because the average person has no clue what differentiates any Asian person - just seeing the same hair, eyes and skin color… and yet in this photograph and in the wall graffiti, the Chinese had easily managed to point out what they see are vast differences between their race and culture.
It's a stereotype. It does mean that there is no basis for truth, but it is an exaggeration of that truth meant to, in this case, belittle the target.
While the real Japanese soldier in the photograph does indeed have a sword slung on his left side like the drawing, and does have the exact same soldier cap, this soldier, at least, does not appear to be wearing glasses, or have grossly over-sized buck teeth.
Also important to note, is that while the propaganda message is written in Chinese and might not be able to be read by the Japanese soldier, its message appears to be quite clear.