Assuming we're dealing with an artificial neural network (e.g. a ConvNet), which was trained by a large dataset of human faces.
Are there any known issues or challenges where facial recognition would fail? I'm not talking about covering half of the face, but some simple common things, such as wearing glasses, a hat, jewelry, having face painting, or tattoos. Can this successfully prevent AI from recognizing the face? If so, what are the current methods for dealing with such challenges?