I'd like to suggest that it doesn't matter if this photograph, recently discovered in North Carolina, actually depicts enslaved children, or if it depicts free or emancipated children. Their unspeakably sad faces and tattered clothing could be read as evidence of a slave regime's brutal cruelty, or it could be something else. Only those children will know for sure.
The bill of sale that accompanied the photograph for a slave named "John" seems to correspond with one of the children, who has also apparently been identified as "John." This provides some evidence for the assumption that these children, or at least one of them, was enslaved at some point, but we don't really know for sure if these children, as they sat for this photograph, were in fact enslaved, free, or recently emancipated.
The assumption that nineteenth-century photographs of Southern blacks depict slaves or conditions of slavery is a pernicious one. Because relatively few photographs of actual verified slaves exist from the pre-Civil War period, historians frequently rely on post-emancipation photographs to provide visual evidence for the conditions of slavery, the assumption being that the material conditions of black life in the South were not vastly different after 1865 than they had been during slavery. Fair enough.
But the implicit assumption that black life is equivalent to slavery, no matter what the era actually depicted, or the actual legal status of the people represented, runs the very significant risk of assigning an immutable association of "slave" to any photographic depiction of nineteenth-century blacks.
This is not to say that historians should not use what photographic evidence is available to them, or that they should ignore the very real fact that the majority of black Americans before 1865 were indeed held in slavery, or that black life in the post-emancipation South did not materially differ in many ways from slavery. Rather, I would argue, the two sad boys in the photo above tell us less about slavery than they do about a broader and richer swath of American history that, yes, includes slavery, but like these children, need not be defined by it.