  This paper deals with the dynamics of discretizations of isometries of
$\mathbf R^n$, and more precisely the density of the successive images of
$\mathbf Z^n$ by the discretizations of a generic sequence of isometries. We
show that this density tends to 0 as the time goes to infinity. Thus, in
general, all the information of a numerical image will be lost by applying many
times a naive algorithm of rotation.
