Many of these studies have used Deep Learning, which gives extremely good results but requires a vast amount of data and computing load.  On the other hand, Machine Learning is faster than Deep Learning and does not have a much-needed computing load, but it does not provide as high an accuracy value as Deep Learning.  Then, traditional feature extractors were combined with pre-trained Deep Learning feature extractors. 
Deep Learning
On the other hand, Machine Learning is faster than Deep Learning and does not have a much-needed computing load, but it does not provide as high an accuracy value as Deep Learning.  In the end, multiple binary classifications were conducted instead of multiclass classification with Machine Learning classifiers. 
Machine Learning