in reply to Re^4: system call in crontab
in thread system call in crontab

If you want to change your X Windows background, feh will need to know the name of the X Windows display to use. It will expect that name to be in the DISPLAY environment variable. If you only have one display on your local system, its value will be ":0.0" so you could use this:
system("DISPLAY=:0.0 /usr/bin/feh --bg-center /home/user/Pictures/rota +te/1.jpg");
or better
$ENV{DISPLAY} = ":0.0"; system("/usr/bin/feh --bg-center /home/user/Pictures/rotate/1.jpg");