https://towardsdatascience.com/learning-note-single-shot-multibox-detector-with-pytorch-part-1-38185e84bd79
https://towardsdatascience.com/learning-note-single-shot-multibox-detector-with-pytorch-part-2-dd96bdf4f434
https://towardsdatascience.com/learning-note-single-shot-multibox-detector-with-pytorch-part-3-f0711caa65ad