Something to consider:
The Buffalo NAS (at least my Linkstation Live 320) has a basic no-frills version of Apache webserver installed in it. This webserver is what serves the configuration pages, and is presumably behind the web access pages as well.
That being the case, it is possible to put HTML files in your web-accessable share, and those files can be handled by your browser just like any website's web pages. About the only thing you can't do is CGI stuff.
Some photo-handling software packages allow you to automatically create an HTML-based slideshow. Adobe Lightroom, for example, can do this. With Lightroom I can upload an HTML based slideshow directly to one of my web-accessable shared folders on the LinkStation, and then email the link to the front page. Anyone visiting the link will be taken to the slide show, complete with thumbnails.
This is a software based solution, of course; your photo handling software must be capable of generating the thumbnails as well as full-sized images, AND the HTML to link them all together.