igp_tag_category_mapping.php

<?php

add_filter( 'igp_image_post_taxonomy_terms', function ( $terms, $image, $post_id, $taxonomy ) {
	$tags = isset( $image->tags ) ? maybe_unserialize( $image->tags ) : array();
	if ( empty( $tags ) ) {
		return $terms;
	}

	$tag_cat_mapping = array(
		'whizalternatives' => 'alternatives',
		'whizlongboards'   => 'longboards',
		'whizmidlengths'   => 'midlength',
		'whizshortboards'  => 'shortboards',
	);

	foreach ( $tag_cat_mapping as $tag => $cat ) {
		if ( in_array( $tag, $tags ) ) {
			$term = term_exists( $cat, $taxonomy );
			if ( $term ) {
				$terms[] = $term['term_id'];
			}
		}
	}

	return $terms;
}, 10, 4 );