At first, you will need a child theme for your parent theme.
Open functions.php of your child theme and add the following code:
<?php remove_action( 'woocommerce_before_single_product_summary', 'woocommerce_show_product_images', 20 ); // conditional logic function for logged-in users function logged_in_images(){ // if user is Logged-in, display original product image if ( is_user_logged_in() ) { echo woocommerce_show_product_images(); } // if user is not logged in, display the placeholder image instead else { echo '<img src="https://via.placeholder.com/150">'; }; } add_action( 'woocommerce_before_single_product_summary', 'logged_in_images', 20 ); ?>
Be sure to change the placeholder with your own default image which you want to select.