You need a pixel density of 40+ pixels for which function?

A pixel density of 40+ pixels per object is typically required for the function of recognition in video surveillance systems. Recognition involves being able to identify specific features of a person or object, such as recognizing a face or a license plate from a distance. This level of detail ensures that the video footage captures enough information to distinguish between different individuals or objects, allowing for accurate identification based on characteristics.

In the context of video surveillance, detection refers to the ability to notice an object or movement within the camera's field of view, but it does not necessarily require high pixel density for basic awareness of presence. Identification, on the other hand, generally requires higher pixel density than 40 pixels to be effective. Recording is simply the act of capturing video data and does not inherently involve pixel density for recognizing or identifying details in the footage. Hence, the specific requirement of 40+ pixels aligns best with the function of recognition, making it the correct choice.