The ghost left it's imprint in all around it.
In the way the water ran down the window pane during a storm, in the shape of the cobwebs in the corners of the room. When you looked at the mournful swirls in the dust on the window sill and the shape of the drapes swishing in the draft. The house wasn't so much haunted as it was the haunting.
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It should have long ago collapsed in decrepitude, but the spirit sustains it as the house gives it a place too dwell and stay linked to this plane. Even the faces in the pictures on the walls all started taking on his features, slowly growing angular jaws and high cheek bones. And soft eyes.