If your hidden images are not appearing as options for pinning, it's possible that your site's thumbnails are too small to be picked up by scraping tools, such as the native Pinterest tools or the Tailwind browser extension.
In this case, you can add the following to your theme's functions.php file to use the medium size image for the Tasty Pins hidden image thumbnails.
Note: This only affects the image that is actually loaded on the page; Tasty Pins includes the data-pin-media image attribute to instruct Pinterest to save the full-size image to Pinterest, regardless of what image is loaded on the page.
add_filter( 'tasty_pins_hidden_image_thumbnail_size', function() {
return 'medium';
});