VGG16 is a built-in neural network in Keras that is pre-trained for image recognition.
Technically, it is possible to gather training and test data independently to build the classifier. However, this would necessitate at least 1,000 images, with 10,000 or greater being preferable.
In this regard, it is much easier to use a pre-trained neural network that has already been designed for image classification purposes.
This is probably the best generally available technique for image classification.