Bug #1648191: typo in docs.

Doc/lib/libimageop.tex

@@ -19,7 +19,7 @@ per pixel, etc.
 
 
 \begin{funcdesc}{crop}{image, psize, width, height, x0, y0, x1, y1}
-Return the selected part of \var{image}, which should by
+Return the selected part of \var{image}, which should be
 \var{width} by \var{height} in size and consist of pixels of
 \var{psize} bytes. \var{x0}, \var{y0}, \var{x1} and \var{y1} are like
 the \function{gl.lrectread()} parameters, i.e.\ the boundary is