Face detection is the first step in face recognition, so face recognition is affected by the same factors as face detection. In addition, the target image should ideally fulfill the following criteria:
Face direction. The face looks directly at the camera, and is not overly rotated.
Face size. The face forms a large proportion of the image.
Facial features. Facial expression, facial hair, and presence of spectacles match the training image as closely as possible.
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