1. A system comprising: a computer programmed to perform an image classification method including the operations of: generating a feature vector representing an input image by unsupervised operations including extracting local descriptors from patches distributed over the input image, encoding the local descriptors extracted from each patch using a Fisher vector encoding, and aggregating the encoded local descriptors to form a vector; and generating a classification value for the input image by applying a neural network (NN) comprising an ordered sequence of layers to the feature vector wherein each layer of the ordered sequence of layers is applied by performing operations including a linear vector projection and a non-linear vector transformation.