podobnou vec jsem resil v bashi, takze to muzes vzit jako inspiraci a upravit si to pro bat

	Kandidatu=`find ~/.fluxbox/backgrounds/ -maxdepth 1 -type f| wc -l`
	number=$RANDOM
	let "number %= $Kandidatu"
	nic=$number;
	let "number += 1"
	nic=$number;
	novy=`find ~/.fluxbox/backgrounds/ -maxdepth 1 -type f| sed -n "$number"p`