  A sliding camera inside an orthogonal polygon $P$ is a point guard that
travels back and forth along an orthogonal line segment $\gamma$ in $P$. The
sliding camera $g$ can see a point $p$ in $P$ if the perpendicular from $p$
onto $\gamma$ is inside $P$. In this paper, we give the first constant-factor
approximation algorithm for the problem of guarding $P$ with the minimum number
of sliding cameras. Next, we show that the sliding guards problem is
linear-time solvable if the (suitably defined) dual graph of the polygon has
bounded treewidth. Finally, we study art gallery theorems for sliding cameras,
thus, give upper and lower bounds in terms of the number of guards needed
relative to the number of vertices $n$.
