How Do Lens Fingerprints Affect Picture Quality?

Not all dirty fingerprints are created equal. :)

A fingerprint on the lens can range from minor nuisance, to significant impact in terms of image quality.

However, in general, any kind of oils will attach dirt and grime over time, so a smudge today can become a dirty blight days later.

In general, using a mild solvent/ glass cleaner works to wipe smudges away; there's no real high-tech approach needed.

However, in some cases, a dome (not lens, but outside bubble) is treated with a hydrophobic chemical like CleanView domes or some Panasonic models. Cleaning domes then requires a bubble replacement, since any contact at all lifts away the anti-rain coating.

From my experience repairing cameras, some fingerprints over the lens usually don´t have a impact on the image quality. the camera will just see/focus through it.

In PTZ domes, even when the bubble has some considerable amount of scratches, the camera will usually see through it. If you have some kind of option to "Near Focus", the camera can focus very near and could focus the scratches.

Fingerprint impact on picture quality can range from none to substantial. They are easy to clean with camera lens cleaning pen.

My guess could be anything from blocking light input to the imager to changing the light input to the imager causing the recorded image to be flawed or blurred. It would depend on severity of course.

A good comparison would be a smudge on your glasses (if you don't wear them ask anyone who does.) Minor particulate can be a minor distraction, but anything above a certain level would be a cause of frustration, particularly oily substances.