 Complete the following phrase:  Two very important daguerreotypes an early photographic process were purchased in the 1990s. The first was of African American abolitionist and former slave Frederick Douglass, acquired in 1990. It is one of only four daguerreotypes of Douglass known to exist. That year, the number of images in the museums photography collection reached 8,500 objects. Six years later, the NPG obtained for 115,000 the earliest known daguerreotype of abolitionist John Brown, whose 