Tutorial on Graph Neural Networks for Computer Vision and Beyond (Part 1)

I'm answering questions that AI/ML/CV people not familiar with graphs or graph neural networks typically ask. I provide PyTorch examples to clarify the idea behind this relatively new and exciting kind of model. To answer them, I'll provide motivating examples, papers and Python code making it a tutorial on Graph Neural Networks (GNNs). Some basic knowledge of machine learning and computer vision is expected, however, I'll provide some background and intuitive explanation as we go. First of all, let's briefly recall what is a graph?