The use of the color histogram pattern (supposedly in grayscale) as an evaluation factor for image matching, in my personal opinion, is not a suitable criterion for a classifier, unless either the size and "color" of those pictures are fairly different, or if you are interested in a fastest algorithm. In fact, I think histogram equalization is nothing more than an image enhancement tool to emphasize some features of the image, but no more than that; Obviously it is a personal opinion, and in the case of image processing there are no general rules, and in your particular case you can even check if it meets the needs, who knows ...By the way, why not use the raw image itself for the neural network ?