+
+The image that it manipulates will be grabbed from the portion of
+the screen underlying the window, or from the system's video input,
+or from a random file on disk, as indicated by
+the \fIgrabDesktopImages\fP, \fIgrabVideoFrames\fP,
+and \fIchooseRandomImages\fP options in the \fI~/.xscreensaver\fP
+file; see
+.BR xscreensaver-demo (1)
+for more details.