How can I earn trading card in Ultra Street Fighter IV?

Recently I open Steam's Inventory and realize that I have 5 trading cards from Ultra Street Fighter IV (1 Decapre, 1 Elena (foil), 2 Poison, 1 Yang - I don't even play these characters much), I have no idea how & why & when did I get them.

I see that there are 10 trading cards for Ultra Street Fighter IV, how can I get them, especially the foil one? Do I need to connect to the internet while I play the game?

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How can I earn trading card in Ultra Street Fighter IV? - Exhibited samples of vintage photos in frames for sale on wall of small local shop

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Does Ultra Street Fighter 4 have all characters?

Ultra Street Fighter IV features 44 playable characters.

How do you get better at Ultra Street Fighter 4?

6 Tips for Playing "Ultra Street Fighter 4"

Try Out All the Characters. I know this goes without saying, I mean it's Street Fighter. ...

Endless Lobby Is Your Friend. ...

Play to Learn, Not to Win. ...

Don't Ultra as You're Getting Up. ...

If It's Been a While, Hit That Training Mode! ...

Just Have Fun! ...

3 Creepy Pok\xe9mon Fan Theories.

Who made Ultra Street Fighter 4?

CapcomDimps

Is Street Fighter IV free?

Play Street Fighter IV Champion Edition free Street Fighter IV Champion Edition is available to play for free.

USF4 BASIC CHARGE TUTORIAL FOR BEGINNERS

Sources: Stack Exchange - This article follows the attribution requirements of Stack Exchange and is licensed under CC BY-SA 3.0.

Images: Artem Beliaikin, Alexander Kozlov, Andrea Piacquadio, Ketut Subiyanto