Nextgen Gallery Images being Pin-able

towards the bottom of the content area of this page (https://www.guitarstorage.com/shop/multi-guitar-stands/) there’s a bunch of thumbnails that link to a Nextgen image gallery.

I want to Pin some of these pics with pinterest. To be clear, I want to pin the full sized images, not the thumbnails. However when i put the URL of that page into Pinterest in the Add Pin>Find Images field where the URL gets entered, it doesnt find any of these 5 images. Nor does it work when i type in the exact url of a specific image.

any idea why that is? please advise. thanks in advance!