WordPressThemeFooterAutoCopyright.php

<?php
// Gets the year of your first published post, the current year, and displays the year range between them.
// If both are the same year, just displays current year. Change "slug" to your theme's domain.

function slug_copyright() {
	$fp_get_all = get_posts( array(
		'numberposts' => 1,
		'post_status' => 'publish',
		'order' => 'ASC'
	) );
	$first_post = $fp_get_all[0];
	$fp_date = $first_post->post_date;

	$fp_year = date( "Y", strtotime( $fp_date ) );
	$cur_year = date( "Y" );

	if ( $cur_year === $fp_year ) {
		$copyright = sprintf( "&copy; %s %s", $cur_year, get_bloginfo( 'name' ) );
	}
	else {
		$copyright = sprintf( "&copy; %s &ndash; %s %s", $fp_year, $cur_year, get_bloginfo( 'name' ) );
	}
	echo $copyright;
}
?>

// Invoke in theme with the following function call in your theme "footer.php" file...
<?php slug_copyright(); ?>