Custom image field for products

I’m trying to create a custom field for products to accept a URL to an image (for example, to show a flag image to represent the country from which the product was made).

As you can see here: http://everyboutique.com/product/silver-silk-dress/ I’ve successfully created a custom text field that says what country (“Location: USA” – Obviously I have a handle on creating custom fields.), but when I create an additional field for a URL, it will save, but won’t display on the front end. This is the code I use to try to display it:

<img src=”<?php echo get_post_meta( get_the_ID(), ‘flag_field’, true ); ?>” width=”19″ height=”13″ />

Any thoughts on what I might be doing wrong?

https://wordpress.org/plugins/woocommerce/