This would be a classifier model, incapable of making images. Most classifier models only output a dictionary of single floating point values for each class it is trained on representing the chance the image belongs to that class. It'd probably be trained by an organization like NCMEC, possibly working with a very well trusted AI firm. For verifying it, usually you reserve a modest representative sample of the database and don't train on it, then use that to determine how accurate the model is and to decide on what score threshold is appropriate for flagging.