Barbara Slingsby (1602-1658) was an ancestor of Talbot. The oil painting portrait of her is by a follower of Peter Lely.
There is a project blog dedicated to this photograph which gives more information on Barbara Slingsby and why Talbot may have thought the portrait was worth taking down from the wall and taken outside to have it's photograph taken.
Image from the collections of the British Library (usage terms: Public Domain)
