Really quite an experience, glad I got to play it.
My main critique would be that the pacing felt a little rushed and having a deeper story/lore would be great ways to expand the concept. Perhaps have the house seem normal for longer or have smaller details out of place that escalate into the stranger events leading up to the blood and the painting.
My current headcanon/theory is that the painting is some lovecraftian corruption that takes hold in a house like a mold, warping reality to insert itself into a room and leaking out weirdness into the home that acts to draw its victim near enough to pull it inside into the twisted mirror dimension that the creature resides in in order to feed.
Overall I really enjoyed the game, it's very well done on tension and atmosphere and it leaves me wanting to know more.