You're looking at a photo from "The Cohabitation Formulation." Raj's sister returns during the episode.
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The Big Bang Theory Season 4 Episode 16 Quotes

Howard: I'm not having this conversation with you Ma!
Howard's Ma: God forbid you get one of those new fancy sex diseases!

Bernadette: I think the woman can manage to put a wig on by herself.
Howard: It's not just the wig, it's pinning her hair up, it's putting on her eyebrows...it's a two person job.