Anyone who wants to know what observations about the man in the middle of the picture identify him as having strong yin will want to examine every aspect of his entire body. It is the appearance of every part of his entire body that indicates strong yin development of the body.
Another way to make a judgement about the likely physical condition and Yin development of the men in the picture is to re-examine them while focusing on the relationship their body has to the rifle they are holding. If a particular example man appears to be holding the rifle it what could be construed as a sexual manner, specifically meaning his body appears to be holding the rifle as if it were holding his penis for masturbation, that individual will likely be of a lesser quality of mental and physical conditioning as well as having a distorted development of the yin part of the body.
There are multiple men in the example picture who appear to be holding their rifles in a sexually suggestive manner for the curious reader to discover. The body of each of those men is distorted in a way that is indicative of distorted physical and mental abilities and distorted yin development of the body, which is a long winded way of saying that the individuals likely to be holding the rifle like a penis are the individuals who exhibit the most severe bodily distortion.