Modern investigators have access to everything from traditional 35mm film to smartphones and full-frame mirrorless cameras, and each behaves differently when faced with low light, fast movement, dust, or reflections.

Analogue cameras work by exposing light onto physical film, which introduces a few quirks that are worth understanding before you trust the results. One of the easiest mistakes is forgetting to wind the film on between shots. This creates a double exposure, where two images are recorded on the same frame, giving that classic semi-transparent figure that has fuelled spirit photography for more than a century. Even today, accidental double exposures remain one of the most convincing-looking false positives.

Film is also sensitive to the condition of the camera and the film stock itself. Old or poorly stored film can develop light leaks or fogging. Small cracks or gaps in the camera body can let in stray light, leaving streaks or patches...