  We introduce three approaches to generate curvature invariants that transform
covariantly under a conformal transformation of a four dimensional spacetime.
For any black hole conformally related to a stationary black hole, we show how
a set of conformally covariant invariants can be combined to produce a
conformally covariant invariant that detects the event horizon of the
conformally related black hole. As an application we consider the rotating
dynamical black holes conformally related to the Kerr-NUT-(Anti)-de Sitter
spacetimes and construct an invariant that detects the conformal Killing
horizon along with a second invariant that detects the conformal stationary
limit surface.
  In addition, we present necessary conditions for a dynamical black hole to be
conformally related to a stationary black hole and apply these conditions to
the ingoing Kerr-Vaidya and Vaidya black hole solutions to determine if they
are conformally related to stationary black holes for particular choices of the
mass function. While two of the three approaches cannot be generalized to
higher dimensions, we discuss the existence of a conformally covariant
invariant that will detect the event horizon for any higher dimensional black
hole conformally related to a stationary black hole which admits at least two
conformally covariant invariants, including all vacuum spacetimes.
