Well you may call it art but the sculptor who did the original would probably think it as graffiti.It would be like me painting a picture over your favourite photo that you had on display !!
@peterlgrave What Bab's is saying is that this is a commissioned piece of art, each tile was made and placed, it took three years to complete and has been there since 1989. See Bab's link above.
@peterlgrave It isn't graffiti Peter it is a mosaic. https://melbournepublicart.wordpress.com/tag/angel/
@onewing Thanks Babs, the other link has slightly different information, this one mentions it being in the National Gallery as you remembered.