When snapping photos, especially in a dimly-lit area, it’s easy to take a picture without noticing the camera’s strap has fallen near the lens. The same goes for the photographer’s finger, hair, or any slight and often linear object, such as a piece of fuzz. This creates what appears to be a long object, often out of focus and/or brightly overexposed that is unfamiliar to the surprised photographer. Often, the subtle design of something like a strap is enhanced to an impressive form. When you find a “streak of light” in your photo, always rule out this possibility first.
Oddly enough, when tiny objects are photographed this way, they sometimes appear slightly translucent, as well. This adds to the ghostly effect. On the other hand, paranormal anomalies sometimes appear in a form very similar to these effects. If you’re a paranormal investigator, it’s best to use a strapless camera (or at least make sure the strap is tightly managed) and pull back long hair.