I think the woman in the portrait is Karen DeGroot. Also I read somewhere about the masks... Let's remember the 19th century mining ship Black Rock that also contained slaves. There is a theory out there circulating (I'm torn about it) that some of the slaves survived and are actually inhabiting the island, ergo the two different sets of Others. Perhaps the masks are because of studies on these people or finds from these people (btw - Mr. Eko was from Africa)
Also - there is a black horse sculpture and let's not forget the black horse that played a significant role in Kate's life, and that she and Sawyer saw on the island (even though it could have come from the Flame)

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