Giffer will never download a GIF from the same URL. However, if the same GIF comes from different URLs (e.g. when two adapters find the same GIF on a different site) then giffer would download both of them.
giffer-md5-duplicates additionaly saves the md5 hash into the database and checks it before saving a new GIF.
giffer.plugin(require('giffer-md5-duplicates'))