in reply to system call in crontab
That command is intended to put an image on the root window of the user running it. However, since a cron job doesn't typically start an X-Windows session, it's a command that doesn't make much sense. If you run it from the "shell", you're actually running it from a pseudo-terminal - try running the command from a console. It won't work then either.
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Seekers of Perl Wisdom