Extracts video IDs from watch, youtu.be, Shorts, embed, live, nocookie, attribution and oEmbed links (and bare IDs, with t= timestamps and playlist parameters), then lists every thumbnail YouTube serves — maxresdefault, sddefault, hqdefault, mqdefault, default and the auto-picked frames 1–3 in each size — as JPG or WebP on i.ytimg.com or the legacy img.youtube.com host, plus watch/short/embed/privacy-embed links, an oEmbed URL and a ready-to-paste iframe. The preview shows the main variants; Download fetches one resolution in the Worker so it can be saved as a file. Links are built locally; images come from YouTube.