I don't think the recognition is the challenge but rather the training of the model. Like imagine taking a really long time to compute a good linear regression

I don't think the recognition is the challenge but rather the training of the model. Like imagine taking a really long time to compute a good linear regression equation, but then to use it you just plug in the values. That said, this deep convolutional neural net for ImageNet with 60 million parameters and 650,000 neurons took 6 days to train on two GPUs [0] [0] http://deeplearning.cs.cmu.edu/pdfs/1028/ImageNet.pdf http://deeplearning.cs.cmu.edu/pdfs/1028/ImageNet.pdf