They are obvious lashings, and they appear to have come from a whip like object. Take a look:
I think this could be easily recreated. It looks like it came from a whip like object while the above young victim was bent forward. He was probably held into place by someone or something and forced to remain standing, otherwise I think he would have fallen to his knees. The guy doing the whipping would have had to throw the whip behind himself and then swing it over his shoulder -- I think that would have created the marks. It also appears that it would have been his right shoulder and the guy doing it was right handed (look at the angle of the lash marks). The typical reaction to something like this is to fall onto the ground in a fetal position and to cover your head.
It also (in my mind) seems consistent with what I know about how such tortures are carried out, as it isn't just one after another. There is a dramatic pause in-between each lashing. It creates a psychological effect on the victim, which is designed to constantly make the victim await and fear the next blow. From my understanding of how the body reacts to being beaten in such a manor you typically stop feeling the intense pain of actually being beaten around the 10-15th blow or so, and it's the psychology behind the beating not the physical pain that is the real point anyway. If you actually watch something like this happen you'll notice that the victim will tense up before being hit or when they think they are about to be hit, they may even holler out. I counted around 30 visible lash marks on his back, and what appears to be a bruise on his side which I would guess came from a boot to the ribs. He might have gotten that if he had fallen to the ground and someone kicked him, and I would assume that it would have likely come from a steel toe boot. Look at that image here:
It appears to be too large to be from a fist. Looking at various pictures, which are not all that good quality it seems to be darker in the center which would indicate that it came from something like a boot or a shoe. I'd guess it likely came at the end of the lashings when he was allowed to fall to the ground and curled up into the fetal position or if he fell to the ground during the lashings into the fetal position. Either way whoever did it was on his left side and he was leaning on his right side or mostly on his stomach. (Otherwise, I think the mark would be up toward his back a bit more.) I think he was probably leaning on his right side, because it's a big bruise and it's difficult to muster a lot of force when your foot is close to the ground. (If you don't believe me try it out.)
I'm not an expert or anything, but if I wanted to recreate those type of wounds which to me appear plausible and real, that is what would I would do and how I would reenact what likely happened.