Introduction
You almost never need to train an image classifier from scratch. Libraries offer dozens of networks already trained on ImageNet's 1.2 million images, ready to download in one line. You can use them directly to recognize the 1,000 ImageNet classes, or fine-tune them on your own classes with just a few hundred or thousand images.
Think of buying a professional camera with good default settings versus building one from parts. The pretrained model is the camera that already works brilliantly; you just adjust a few settings for your particular kind of photography.
This topic puts the transfer-learning ideas from the Training tab into a complete, practical workflow.