As a reminder: Garland, Napier and Hart had coerced Emery into falsely confessing to Hannah’s murder (which was actually ordered by Napier) in order to protect Correction’s secret. The activist group Pilgrims of Justice, along with a CIA whistleblower (which turned out to be really a CIA factory), had faked footage of Shaun abducting Hannah to prompt his high-profile arrest and its later release when they released the real video and Exposed Correction. Frank Napier couldn’t afford Correction to be exposed, so he had Hannah killed and Shaun was framed for the murder.
Armed with the bus footage, Carey had blackmailed Napier, Garland and Hart into telling him the truth by threatening to send him to the Crown prosecutor, thus invalidating the false confession Shaun Emery had made under duress after Napier kidnapped his young daughter. Garland and co. thwarted Carey’s blackmail attempt by using the magic of technology to corrupt the file he was able to download at a pre-arranged time. “I’m sure you made copies,” Garland told Carey, and she was right.
In second series, episode two, Commander Hart asked Garland if she trusted Carey. She didn’t and cited “what we found” as the reason. Hart replied, “It was insurance you would do the same.” What Garland and Hart found, we learn at the end of episode three, was Carey’s hidden insurance, the memory card in the picture frame also containing a photo of a young Rachel and her mother.
For context as to the meaning of the photograph: Rachel’s mother died of lymphoma when Rachel was 13, after which her father moved her into the other secret family he had had for years. Abigail, who comes to stay with Rachel in her bugged and secretly filmed apartment in season two, episode three, is her half-sister in this family. It’s no wonder the stubborn DCI can’t stand being lied to.