the Daguerreotype is a type of photography developed by Louis Daguerre. it is a photo printed in a combination of Mercury and Silver, making the photo almost mirror-like. it was popularized around the 1840's in the United States.
Louis Agassiz photographed the blacks that are nude to show the differences between the race, ultimately that blacks were inferior. the black female in the nude is an enslaved teenage girl named Delia. the male is unnamed (possibly Renty?) but it is noted that he is from The Congo.
those photos in particular are the most striking to me. aside from the fact that they're degraded, especially Delia, by being stripped to the waste (the man was completely nude, although i could not find the photo), the eyes say so much. but the faces of all the blacks speak volumes really, not just the eyes. they're rebellious and painful and angry and twisted all at the same time.