後ろ and 裏: behind a person and on an object’s reverse side
Separate a position behind someone in a line from the back of an envelope, then examine overlap behind a building.
Behind a reference person or object
後ろ, read うしろ, locates something behind a person or object. 私の後ろに並んでください。 asks someone to line up behind the speaker.
椅子の後ろに鞄を置きました。 says that a bag was placed behind the chair. It does not say the bag was attached to its back surface.
A reverse surface or the back of a building
裏, read うら, can name a reverse surface or a building’s back area. 封筒の裏に住所を書きました。 says that an address was written on the back of the envelope.
建物の裏に小さな庭があります。 says that a small garden lies behind the building. Here 裏 is an area rather than a sheet-like surface.
Checking for a surface or a surrounding position
写真の裏を見ました。 says that the reverse side of a photograph was examined. It does not describe looking at a person standing behind the photograph.
建物の後ろ and 建物の裏 can overlap when locating something behind a building. That interchange does not extend mechanically to lining up in 私の後ろに並ぶ.
Does カードの裏に番号があります。 put the number on a separate object behind the card?
Show the answer and why
No. The sentence places the number on the card’s reverse side.