Besides being the role of female actress Juliette Lewis in the Oliver Stone film "Natural Born Killers" there is more than one artist with this name (see links in the Wiki sources):
These are photos from concerts where Mallory Knox played, so they may be of other bands that played the concert as well.
ONE OK ROCK / Mallory Knox / Tonight Alive Dec 12, 2014 Hamburg, Hamburg, Germany Uploaded by Fuyuderpilz
Mallory Knox / Every Time I Die / The Story So Far / A Day to Remember Feb 12, 2014 London, England, United Kingdom Uploaded by Dan Delaney