Ask HN: Why there are two gmail's profile pictures?

Although in order to get the right answer I should rephrase this as a wrong statement instead of a question

So .. when you are browsing a gmail thread, there's a small picture right next to the senders' name.. Now if you hover that picture, a small contact card opens, which also contains a picture..

I've seen quite a few behaviors and I'm curios about why it does what it does:

- a profile picture vs a different contact picture - a profile picture vs a no-picture icon - a no-profile icon vs a contact picture - and rarely, a profile picture vs the same contact picture