Neural Network for classifying humans
In Part 1 of this "tutorial/discussion" ther is a good explanation of the problem and a possible solution using OpenCV built in Haar Cascades  or HOG for Human Detection (this is the key-word you should use to search info about your task).

They are both really fast compared to NN and require little training.

In Part 2 are explained more modern approaches using Deep Learning. A notable mention would be AlexNet.

At the end there is even a tutorial on Setting up a Basic Human Detector with Tensorflow.