What is the religious ruling on a colleague who stole my email, which contains photos of my wife without a headscarf and private correspondence, and is stealing these photos and papers to blackmail me with them?

What your colleague did is forbidden (haram) because it combines several transgressions: betrayal of trust, bad neighborliness, spying on Muslims, prying into their private affairs, and terrorizing them with threats. These are ugly acts and clear injustice, and their consequence is severe in this world and the hereafter, due to the Prophet's (peace be upon him) saying: "There is no sin more deserving for Allah to hasten the punishment for its perpetrator in this world, along with what is reserved for him in the Hereafter, than oppression and cutting off ties of kinship." The questioner should be cautioned about his mistake of photographing his wife, as this is likely to expose her to others. He must strive to stop this wrongdoer from his injustice.