screen capture with scrot

[Alberto José Rodríguez Rodríguez <ajrodriguez blulabs es>]

Hi, I have a script using scrot (a shell program based on Imlib2) for
regular screen captures and usually it works well, but in some
executions of gnome-shell it always captures the same image, the first
capture did. It's very frustating. Could it be some kind of
incompatibility between scrot and gnome-shell?

P.S. I'm not using the ShellDbus service for screen capture because it
blocks the painting for a few seconds.