We are trying to learn a good metric of distance between images using deep convolutional neural netowrks, which can be then applied to image classification based on the classsic knn method.
orls_faces文件夹是ORL face database 人脸识别数据集 the Olivetti Research Laboratory in Cambridge, UK 40个类别，每个类别10个样本 PGM格式，92x112的8位灰度图。
F. Samaria and A. Harter "Parameterisation of a stochastic model for human face identification" 2nd IEEE Workshop on Applications of Computer Vision December 1994, Sarasota (Florida).
http://www.cl.cam.ac.uk/research/dtg/attarchive/facedatabase.html
load_all_data() 返回所有的数据，返回数据是list，包含40个list元素，每个list包含同一个类别的10个np.matrix(112x92,dtype=uint8) [[np.matrix(112x92),...],...]