Includes alt text on a Tasty Pins hidden image if none yet exists.

tasty-pins-alt-text.php

<?php
/**
 * Includes alt text on a Tasty Pins hidden image if none yet exists.
 *
 * @param string  $image_content Image content HTML string.
 * @param integer $hidden_image  Hidden image ID.
 * @return string
 */
add_filter(
	'tasty_pins_hidden_image_html',
	function( $image_content, $hidden_image ) {
		$alt_text = get_post_meta( $hidden_image, '_wp_attachment_image_alt', true );
		if ( ! $alt_text || false !== stripos( $image_content, 'alt="' ) ) {
			return $image_content;
		}
		return str_replace( '<img ', '<img alt="' . esc_attr( $alt_text ) . '" ', $image_content );
	},
	10,
	2
);