My theme includes a specific template for image galleries - The Pinterest icon shows up on both posts and pages correctly, but it doesn't show up at all with WordPress generated galleries with the gallery template.
Page (works): http://chicagophoenix.com/galleries/
WordPress Gallery in Gallery Template (doesn't work): http://chicagophoenix.com/galleries/gallery-freedom-to-marry-reception/
It also doesn't seem to work on the Fancybox popup (click on one of the images from the link above). As these are the large images, it'd be ideal for it to appear on those photos and not the smaller ones in the articles.