In reading and interpreting this story, I would call attention to the style in which Hemingway writes it. Notice the verbs in these 4 sentences that describe the picture: “is,” “look,” “are,” and “does not show.” None of the verbs offer action, all are as laconic as the character. Notice too the straightforward, simple construction of the sentences: the 2nd, 3rd, and 4th sentences consist of subject, verb, and modifier, not even containing a direction object: nothing happens in them to anything. The first sentence is even weaker, beginning with the expletive “there is,” which postpones the meaning of the sentence, putting it in the subordinate clause “which shows….” In short, while the sentence communicates the lack of meaning in Kreb’s life, his inability to find romance and sentimentality in the war (as, perhaps, his parents and his town would prefer), its style and structure reinforce the same—and this is the beauty and complexity of Hemingway’s writing. It is also something he associated with manhood: eschewing the sentimental in favor of seeing things “as they are” and telling about that simply, directly, with as few words as needed.
The picture reflects an aura of greyness and anonymity - "the German girls are not beautiful", and although the group was photographed on the Rhine, "the Rhine does not show in the picture". It is symbolic of Krebs' experience in the war, for although he was at Belleau Wood and other famous engagements, he had just done "the one thing, the only thing for a man to do". His experience was devoid of excitement and romance, nothing like what those at home believe it to have been. In fact, Krebs reads with interest accounts "about all the engagements he was in" in histories, where he could "really...learn...about the war".
The colorless banality of the picture also reflects the feeling of numbed nothingness that envelops Krebs upon his homecoming.