Sneakers representation learning
Best is to start from pre-trained encoding. Please check TFHub (https://tfhub.dev/google/collections/image/1).
I have worked myself with encoding of shoes for a sport fashion companies. Remember that there are many different ways images might be seen as being similar, e.g. shape, color(!) etc... You might need to make a pre-processing choice first to drop some aspects, such as working with gray images, blurring some patterns on the shoes etc...