Everything about this picture is right: the colours in both foreground and background, the out-of-focus background, the impracticality of Björk's clothing (which redeems the crochet from its awful 1970s associations), her posture, the asymmetry in her dress, hair and eye makeup. The asymmetric makeup perfects the picture. The human face is asymmetrical and pictures of faces doctored to make them look symmetrical are worrying. Exaggerations of their natural asymmetry are pleasing.
The evil Zorg, Luc Besson's creation in The Fifth Element, played by Gary Oldman (above), with his radically asymmetric hairstyle, would have looked more menacing with a centre parting. That may be what Blake meant by "fearful symmetry". If not fearful, symmetry is uncanny - here is Björk again
It's thought that biological asymmetry arises from the accumulation of genetic and environmental pressures in human development. The perception that perfect symmetry is uncanny may be a sense that a perfect face cannot be human. Perfect human replicas appear to be almost but not exactly like human beings, and are unpleasant to look at. There is supposed to be a zone between the obviously non-human and the obviously human - the so-called uncanny valley - that elicits this disquiet. The metal robot C3PO was charming, but humanoid robots are creepy. This perfect actroid is in the uncanny valley.
Conversely, the face decorations illustrated in Hans Sylvester's Natural Fashion: Tribal Decoration in Africa, (below) are asymmetrical and also have a disregard for precision, which has a comparably pleasing effect. They appeal not as primitive but as human.