I think that the used technology described in CSAM Detection Technical Summary (the so called NeuralHash) is a really bad idea, basically it uses the output of a neural network (likely a CNN) trained using the now classical triplet loss (see page 5). The problem with those methods that they are not always reliable, for instance the same type of networks and same training procedure is used in neural face recognition that proved to be vulnerable (A recent example is the 'Master Faces' That Can Bypass Over 40% Of Facial ID, etc).