  Let $P$ be an orthogonal polygon. Consider a sliding camera that travels back
and forth along an orthogonal line segment $s\in P$ as its \emph{trajectory}.
The camera can see a point $p\in P$ if there exists a point $q\in s$ such that
$pq$ is a line segment normal to $s$ that is completely inside $P$. In the
\emph{minimum-cardinality sliding cameras problem}, the objective is to find a
set $S$ of sliding cameras of minimum cardinality to guard $P$ (i.e., every
point in $P$ can be seen by some sliding camera) while in the
\emph{minimum-length sliding cameras problem} the goal is to find such a set
$S$ so as to minimize the total length of trajectories along which the cameras
in $S$ travel.
  In this paper, we first settle the complexity of the minimum-length sliding
cameras problem by showing that it is polynomial tractable even for orthogonal
polygons with holes, answering a question asked by Katz and Morgenstern (2011).
We next show that the minimum-cardinality sliding cameras problem is
\textsc{NP}-hard when $P$ is allowed to have holes, which partially answers
another question asked by Katz and Morgenstern (2011).
