Museum tech roll call! I picked up leaflet for the same purpose and it's worked great - http://collections.artsmia.org/art/1218/olive-trees-vincent-...

The Rijksmuseum "Rijksstudio" site has been around for a few years and adopted leaflet very early on for image viewing: https://www.rijksmuseum.nl/en/rijksstudio/artists/rembrandt-...

Perhaps of interest to this sub-thread is "IIIF" (the international image interoperability framework), an attempt to standardize access to images (and collections of images) with a JSON(-LD) metadata model: http://iiif.io/