Display featured image with alt

featuredimage.php

<?php

/**
 * Show post thumbnail width alt
 *
 * @author Urban Sanden <urban@sprintworks.se>
 * @param type|string $size Size like 'full', 'large', 'medium', 'thumbnail'.
 * @param type|object $post Post object.
 * @param type|string $fallbacksize_x Fallback image size x.
 * @param type|string $fallbacksize_y Fallback image size y.
 * @param type|string $fallbacktext Fallbacktext.
 */
function showPostThumbnail( $size, $post, $fallbacksize_x = '200', $fallbacksize_y = '200', $fallbacktext = 'Bild saknas' ) {

	// Get featured image id.
	$featured_image = wp_get_attachment_image_src( get_post_thumbnail_id( $post->ID ), $size );

	// Get image alt text.
	$image_alt = empty( get_post_meta( get_post_thumbnail_id( $post->ID ), '_wp_attachment_image_alt', true ) ) ? get_the_title( $post->ID ) : get_post_meta( get_post_thumbnail_id( $post->ID ), '_wp_attachment_image_alt', true );

	// Display image, or fallback image.
	if ( $featured_image[0] ) : ?>
		<img src="<?php echo esc_url( $featured_image[0] ) ?>" alt="<?php echo esc_attr( $image_alt ) ?>">
	<?php else : ?>
		<img src="<?php echo esc_url( sprintf ( 'http://dummyimage.com/%sx%s/cccccc/ffffff/ccc.jpg&text=%s', $fallbacksize_x, $fallbacksize_y, urlencode($fallbacktext) ) ); ?>">
	<?php endif;

}

Usage:

<?php showPostThumbnail('large', $post, '170', '120'); ?>

or

<?php showPostThumbnail('large', $post, '170', '120', 'Missing image'); ?>