How does Ted Hughes use imagery in Perfect Light?

In Lines 18-20, the phrase "Failed to reach the picture" refers to the "knowledge" in line 15 and reemphasizes the fact that neither the speaker nor the camera knows what the woman said to her daughter. The speaker personifies time with military imagery, saying it comes toward her "like an infantryman / Returning slowly out of no-man's-land." The location of noman's land is significant because it means the land between two warring parties, suggesting that the woman is caught up in the middle of her own private war, though what its cause is or who the armies are is not revealed.