Choosing the threshold will be hard. And (as mentioned by other poster) the model is unlikely to generalize well to classes of data it has not seen. I suspect t

Choosing the threshold will be hard. And (as mentioned by other poster) the model is unlikely to generalize well to classes of data it has not seen. I suspect that this approach will get things similar to numbers wrong quite often, like handwritten characters (a,b,c). Including these into the training set is much more likely to yield a model which will successfully discriminate it.