Just because you hear a creak in the house, or think you see something paranormal, it could be a house settling or some living thing that moved, or an object that resembles a former living being.
I received an email and this photo through facebook from someone who was going to purchase the house this photo was taken in. This is a picture of the attic, and the person thought they saw a ghostly dog in the attic and took the photo. If you look to the right side of the photograph, you can see that the spiderwebs actually form an outline that resembles a dog's face, but it is the spiderwebs!
Keep in mind that if you're looking for something paranormal your mind can trick you into thinking that you're seeing something. It's always good to try and debunk whatever you can. Those that can't be explained are likely paranormal!