> You would have to locally cache the pic and then never clear the cache

I’m thinking something like this:

1. Receive and store (cache) all profile update events.

2. Allow user to “pin” a particular pic image, but continue to receive and store updated profile events. That is, in client-side storage, map the npub to the note id with the pinned profile pic.

3. When a follow’s profile updates, show “<name> has a new profile pic” as a notification like any other. The notification UI can have a pin/unpin button or something to allow the user to decide whether to accept the new pic as the pinned one.

4. When viewing an npub’s profile, show the gallery of previous profile pics. Allow client to pic one to pin. Or “unpin” to always use the latest profile pic.

Notably, Telegram shows users’ prior profile pics. I don’t think it gives users the ability to pin other users’ pics (for their own viewing), but it does preserve the history of pics you can look through.