During a recent investigation Mike took the following photograph...

Now, in this context it's pretty obvious as to what they are. These are what's known as 'lens flare' and occur when a strong light enters the lens and reflects on the internal lenses to create a second 'ghost image' of the light source. Even if the photo itself does not contain any intense light sources, stray light can still enter the lens if it hits the front element.

The example above shows a lens flare created by an internal, powerful lightbulb but this is just one form. There is another type of lens flare that is specific to the digital camera and occurs when the sun is shining directly onto an unprotected lens. Even if the sun is out of shot, if it is directly in front of the camera a group of small rainbows or rainbow-coloured shapes can appear. This type of lens flare is formed by an internal diffraction on the image sensor and acks like a diffraction grating.

So when you're out taking photos of an allegedly haunted location and a small rainbow-coloured anomaly appears in the image always check as to where the sun is in relation to the camera angle. If the sun was directly in front then all you've captured is a digital camera specific lens flare.

More info:
http://www.cambridgeincolour.com/tutorials/lens-flare.htm
http://en.wikipedia.org/wiki/Lens_flare