Telegram keeps your previous profile pictures in a separate album, visible to everyone.
You can see them by opening the settings panel, and clicking/touching your current profile picture there. From this album you can delete them individually.
To me this is kind of a hidden UI. Maybe it's common knowledge, but I decided to post just in case someone's not aware of this feature, and doesn't want an old picture publicly visible.
@BalooUriza I understand that use, but keeping an old profile picture around shouldn't be a thing without explicit consent.
Some folx I've spoken with also say it's useful to keep a history of 'sona art they use for profile pics, and that's a fair point as well.
My main gripe with this feature is how Telegram isn't clear in its UI about its existence... and that will catch people dealing with creeps/abusers by surprise at the worst times.