Discord PFP Grabber

An avatar lives at `https://cdn.discordapp.com/avatars/{user_id}/{avatar_hash}.{ext}`. The hash is not derived from the image - it is an opaque identifier Discord assigns, and it changes every time the user uploads a new picture. An old hash stops resolving once it is replaced, which is why saved avatar links eventually break.

The extension depends on the hash itself. A hash beginning with `a_` marks an animated avatar and must be requested as `.gif`; anything else is `.png`. Requesting a static hash as .gif returns an error, and requesting an animated one as .png gives you a single frozen frame - occasionally what you want, but rarely by accident.

The `?size=` parameter accepts powers of two from 16 to 4096. It cannot invent detail: Discord stores a maximum of 1024x1024 for avatars, so asking for 4096 returns an upscaled image rather than a sharper one.

Every account has an avatar even when the user has never uploaded one, because Discord assigns one of its coloured default images. Those live at `https://cdn.discordapp.com/embed/avatars/{index}.png`.

How the index is calculated changed with the move away from discriminators. Legacy accounts that still have a four-digit discriminator use `discriminator % 5`, giving five possible defaults. Accounts on the new username system use `(user_id >> 22) % 6`, giving six. Code that only implements the old formula returns the wrong default for any modern account.

Discord downscales and crops avatars to a circle for the message list, hiding the original resolution. The full CDN image preserves the upload quality.