I would say that it is a great method to learn proportions, maybe line quality too since you can be confident with your strokes. That said the only issue that the art community has with tracing is when people trace over others work be it a photo or worse another illustration and then don't credit the original artist. It's more of an issue with not crediting the original artist than it being a bad way of learning. It should be fine in this instance because these photos are meant to be learning tools.
