VOTT is a UI for the the registry specialised on tutorial-style material. See http://wiki.ivoa.net/internal/IVOA/InterOpMay2016-EduIG/curation.pdf for a bit of background and http://wiki.ivoa.net/internal/IVOA/InterOpMay2017-EDU/edumatters.pdf for the rationale for later updates. This updates itself on request from the registry endpoint configured in q.rd. It also generates thumbnails for the remote documents, which happens within res/makeThumb. The thumbnails are cached in cacheDir/vott_thumbnails just remove what's in there to start a global recreation (which may take a little while).