When taking photographs during a paranormal investigation, it is important to know the short comings of your camera, as well as the important features. This is in order not so much to avoid contamination or anomalies, because those are a fact of life with digital photography, but to determine whether or not the anomalies are caused by your camera.
Most of the time you will be taking photographs with your camera in automatic mode, which activates the flash. Set your camera to the highest mega-pixel resolution that your camera is capable of when doing so. Does the number of pixels affect the quality or likelihood of capturing an apparition? Not at all; but it does allow you to zoom in on critical sections of your photographs for closer examination without losing clarity of the image the closer you zoom in.
What is more important than pixelization is the amount of memory your camera is capable of storing data to and how you download your camera’s images to your PC for analysis. Memory sticks (flash memory) are getting quite inexpensive, and can be used over and over again (the beauty of digital photography that you’re not paying for film to be developed). So get the largest size memory card you can afford, and if at all possible get a second or third memory card as a backup, because the more mega-pixels you have, the more memory it requires, and the less number of photos you can take.