To deface is defined as to spoil the appearance, mar or disfigure.(verb)
When you draw graffiti over a beautiful piece of art, this is an example of when you deface the art.
See deface in Webster's New World College Dictionary
See deface in American Heritage Dictionary 4
transitive verb de·faced, de·fac·ing, de·fac·es
Origin: Middle English defacen
Origin: , from Old French desfacier
Origin: : des-, de-
Origin: + face, face; see face.
Learn more about deface