Convolutional Neural Networks - Where should I start from? I will soon be starting a part-time job within a start-up and I've been assigned to a project where I'll have to build a CNN that recognizes and counts people in various kinds of videos.

My CEO knows I have no training or experience in Computer Vision and he suggested that I should spend all my working hours in the first month on understanding the necessary concepts behind CNNs and then proceed with the implementation for the next two months.

I know that mathematics are a huge part of understanding the necessary concepts. I'm a CS 3rd year undergrad and my relevant studies in math are comprised of the following:




Calculus $I - IV$
Linear algebra and differential equations (didn't study partial differential equations)
Complex analysis




I've managed to pass these courses with maximum scores. Since mathematics is a very dear interest of mine, I spent a lot of time on actually understanding each and every concept I've studied so far.

So, my questions is, are there any textbooks on CNN(preferably free) you could recommend, given my experience and goal?

Also, since my mathematical training may not be enough, I would also appreciate insights (or textbooks) on what should I learn, or improve while studying the concepts behind CNNs.
I know this is a link only answer, but the question is a reference request.

Neural Networks and Deep Learning is a free online book. The book will teach you about:  


Neural networks, a beautiful biologically-inspired programming paradigm which enables a computer to learn from observational data 
Deep learning, a powerful set of techniques for learning in neural networks