Display a lightbox of the product catalog image, rather than linking to the product page. Drop this code snippet into the bottom of your theme's functions.php file. Implementation note: at line 25 we're stripping the image dimensions out of the original image source in order to try and display the full sized image. So if the catalog thumbnail is…

wc-catalog-lightbox.php

<?php

// Code to display catalog images in a lightbox follows:
add_action( 'wp_enqueue_scripts', 'frontend_scripts_include_lightbox' );

function frontend_scripts_include_lightbox() {
	global $woocommerce;

	if ( is_shop() || is_product_category() ) {

		$suffix      = defined( 'SCRIPT_DEBUG' ) && SCRIPT_DEBUG ? '' : '.min';
		$lightbox_en = get_option( 'woocommerce_enable_lightbox' ) == 'yes' ? true : false;

		if ( $lightbox_en ) {
			wp_enqueue_script( 'prettyPhoto', $woocommerce->plugin_url() . '/assets/js/prettyPhoto/jquery.prettyPhoto' . $suffix . '.js', array( 'jquery' ), '3.1.5', true );
			wp_enqueue_script( 'prettyPhoto-init', $woocommerce->plugin_url() . '/assets/js/prettyPhoto/jquery.prettyPhoto.init' . $suffix . '.js', array( 'jquery' ), $woocommerce->version, true );
			wp_enqueue_style( 'woocommerce_prettyPhoto_css', $woocommerce->plugin_url() . '/assets/css/prettyPhoto.css' );
		}

		ob_start();
		?>
		$( 'ul.products li a:not(.button)').each( function() {
			var src = $( this ).find( 'img' ).attr( 'src' );

			$( this ).attr( 'href', src.substr( 0, src.lastIndexOf( '-' ) ) + src.substr( src.lastIndexOf( '.' ) ) );
		});
		$('ul.products li a:not(.add_to_cart_button)').prettyPhoto();
		<?php

		$javascript = ob_get_clean();
		$woocommerce->add_inline_js( $javascript );
	}
}