Even if all the fonts are rigorously identical the viewing conditions won't be. There will be plates seen at various angles, bent plates, dented plates, dirty

Even if all the fonts are rigorously identical the viewing conditions won't be. There will be plates seen at various angles, bent plates, dented plates, dirty plates etc. I think that if you're going to use a net you should try to train it in such a way that it learns to generalize the fundamental shape characteristics of the characters, much like the human visual system does, and that requires training with a wide range of different type of characters, all considered to be of the same class. If you're convinced that you only need to deal with identical characters you're probably better off using some form of template matching. But I think this is rarely the case for real world systems.