In the poem "Snaps," how does Espaillat use conventional scenes and images to reveal them as oppressive settings in gendered identity?

In "Snaps," Espaillat starts with a series of snapshots of a girl that symbolize the way in which she presented one reality to the camera while harboring a different reality. The conventional scene of her as a child, "neatly dressed...in your white middy," presents the image of the perfect girl, who, dressed in white, radiates innocence. In the next snapshot, the girl appears in a conventional pose as a "nice girl with ankles crossed, hands in your lap's small bounded nest." In the metaphor in this line, the girl's lap is a nest, conveying the idea that women's sexuality is contained. 
Capturing these oppressive images, however, the camera catches the "strain/behind its ease," meaning behind the ease of the girl's "obedient pose." The way in which the camera catches the girl's secret ideas is compared, through a simile, to a situation "as if a passage in some plain old book opened into an unexpected place." In other words, the camera captures something unexpected. The tone of this stanza represents a shift from a feeling of oppression to a feeling of openness and exploration. 
The poet uses the girl's body language as a symbol of the girl's defiance, including "the sharp tilt of jaw" and the "small thrust of hip and shoulder." These subtle body movements and gestures represent the girl's hidden defiance. In the last stanza and the last line of the penultimate stanza, the poet refers to "something sleeping" in the girl that is now flashing the poet "a sign," many years later, of the girl's eventual rebellion. The "something" is a personification and a metaphor of the ways in which the girl will eventually go against the oppressive gender identity she was raised with.