A method of processing image data representative of an image using a multi-stage system comprising a first neural network (NN) for identifying a first image characteristic and a second NN for identifying a second image characteristic. The method comprises processing the image data using t a first at least one layer of the first NN to generate feature data representative of at least one feature of the image and processing the feature data using a second at least one layer of the first NN to generate first image characteristic data indicative of whether the image includes the first image characteristic. The feature data is transferred from the first NN to the second NN. The feature data is processed using the second NN to generate second image characteristic data representative of whether the image includes the second image characteristic.