I do not remember what inspired the idea but it came while watching The Aristocats (coming right after a post based on The Rescuers, one might conclude I am watching old Disney movies; one would be correct). I realize now that it bears some resemblance to a quest in Oblivion but that was not in mind until I started typing this post.
The idea is simple: a painting serves as a window into ours or another world. The fantastic properties of the painting lie undiscovered for some time because the painting remains fixed in place, hanging on the wall of a manor. Rumors of ghosts and possession have, in the past, risen up due to perceptions of movement in the painting but they were often attributed to the house in general and no specific investigation of the painting was made.
The use of such a painting is quite obvious: as a window providing view into another plane of existence, it can be used to explore and investigate this world. Whether the painting updates its view continuously (if I take it down from the wall, does its face change instantaneous to depict the altered perspective into the other world) or gradually (you have to hang it on another wall to get another view) is up for debate. Whichever serves the ultimate purpose of the painting is fine.