  String covers are a powerful tool for analyzing the quasi-periodicity of
1-dimensional data and find applications in automata theory, computational
biology, coding and the analysis of transactional data. A \emph{cover} of a
string $T$ is a string $C$ for which every letter of $T$ lies within some
occurrence of $C$. String covers have been generalized in many ways, leading to
\emph{k-covers}, \emph{$\lambda$-covers}, \emph{approximate covers} and were
studied in different contexts such as \emph{indeterminate strings}.
  In this paper we generalize string covers to the context of 2-dimensional
data, such as images. We show how they can be used for the extraction of
textures from images and identification of primitive cells in lattice data.
This has interesting applications in image compression, procedural terrain
generation and crystallography.
