The physical features would be difficult to impossible to distinguish. I suspect that dress or language/dialect would have been the principle ways in which the peoples of this time and place differentiated from each other.
To correct the above: The Celts were not 'Gallic', but from central Europe; the Angles were Germanic; the Vikings were Scandinavian, and the Picts were something else altogether. The Vikings were known for their great height and large stature. Blond hair would have been predominant among the Vikings; slightly more common than dark hair among the Picts. Manners of dress would have been very different among the four groups you mention.
To correct the above: The Celts were not 'Gallic', but from central Europe; the Angles were Germanic; the Vikings were Scandinavian, and the Picts were something else altogether. The Vikings were known for their great height and large stature. Blond hair would have been predominant among the Vikings; slightly more common than dark hair among the Picts. Manners of dress would have been very different among the four groups you mention.
To correct the above: The Celts were not 'Gallic', but from central Europe; the Angles were Germanic; the Vikings were Scandinavian, and the Picts were something else altogether. The Vikings were known for their great height and large stature. Blond hair would have been predominant among the Vikings; slightly more common than dark hair among the Picts. Manners of dress would have been very different among the four groups you mention.