Hi, deep learning frameworks like Pytorch and Tensorflow come with state-of-the-art image recognition models (VGG, GoogleLeNet, ResNet, Inception etc.) already pre-trained on ImageNet, so one can just download and use them straight away.
This provides a solid starting point as these models have already learnt how to classify objects really well. Transfer learning can then be used to fine-tune them for a specific task like identifying ivory in photos. This just requires that you tweak the existing model a bit and train it on a smaller custom dataset of the image’s/categories you would like to classify.
Hope that helps!