The product URL is: http://nicdim.dscloud.me/wordpress/product/photo-purchase/
It’s an incredibly slow test server, but hopefully it loads for you.
It’s a very simple home written plugin.
The complete shortcode in the product description (in case there’s some conflict) is
[flickr-woo textbox=”photo_ids” showunselectall=true ]
the code behind rendering the button is very simple and just doing an echo
$WOO_SHOW_UNSELECTALL = true;
echo ‘<button class=”btn btn-sm btn-primary image-unselectall”>Unselect all</button>’;