gistfile1.phtml

<?php

$sample_gallery_images = get_custom_field( 'sample_gallery_images' );

// If field value is empty don't output anything
if( ! empty( $sample_gallery_images ) ){
	// If it's an array that means there are multiple images
	if( is_array( $sample_gallery_images ) ){
		foreach( $sample_gallery_images as $gallery_image ){
			// This outputs an image with a link to the image itself with a line break after each image
			echo '<a href="' . $gallery_image '" target="_blank"><img src="' . $gallery_image . '" class="some_custom_class" /></a><br />';
		}
	// Otherwise it's a single image URL
	} else {
		// This outputs an image with a link to the image itself
		echo '<a href="' . $sample_gallery_images '" target="_blank"><img src="' . $sample_gallery_images . '" class="some_custom_class" /></a>';
	}
}
?>