This site calls the photos part of a propaganda campaign:
http://trilogy.brynmawr.edu/speccoll/quakersandslavery/commentary/themes/white_slaves.php
"The tremendous success of the "White Slaves" propaganda campaign has been under increasing scrutiny in recent years. Scholars of history, photography, and cultural studies have formulated a number of interesting arguments to explain the appeal these images may have had for contemporary viewers.
In "Rosebloom and Pure White, Or So It Seemed," Mary Niall Mitchell points out that by depicting slaves as white, the photographs made an argument for the Civil War that was independent of class status. Southern slavery was a threat to the freedom of all white people, the photographs insisted; thus repudiating the notion, made dangerous by the New York draft riots of 1863, that the Civil War was purely an elitist conflict waged with the blood of the poor (Mitchell 58) In the same article, Mitchell also highlights the significance of the fact that the majority of the photos in the series were portraits of young, white, and well-dressed girls. Such portraits took advantage of the patronizing tendencies of the northern Victorian public, calling upon the viewer to protect the purity, innocence, and "whiteness" of youthfulness and femininity (Mitchell 72).
In "Visualizing the Color Line," Carol Goodman notes that much of the power of the photographs stemmed from allusions to physical abuse. When paired with a related article in the same issue of
Harper's Weekly, the allusions in the portrait of white slaves to the white masters' sexual exploitation of their female slaves is clear. The most grievous sin of slavery, the editor of
Harper's Weekly contends, is that it permits slaveholding "
'gentlemen' [to] seduce the most friendless and defenseless of women". Moreover, two of the four black slaves included in the publicity tour bear the marks of abuse on their skin--
Wilson has a brand upon his forehead;
Mary, as she is described in
Harper's Weekly, has more than 50 rawhide-scars on her arm and back. (Goodman)
Gwendolyn DuBois Shaw, in
Portraits of a People, considers the ways props were used to imply that the subjects shared the viewers' values. Several portraits taken by Charles Paxson figure the American flag prominently in the composition, such as
"Freedom's Banner." Another of Paxson's photographs,
"Learning is Wealth," depicts each of the subjects holding a book--which, moreover, recalls the purpose behind the whole project, raising money for schools in Louisiana. (Shaw 160)."