Following

A struggling, unemployed young writer (credited as "The Young Man") takes to following strangers around the streets of London, ostensibly to find inspiration for his first novel. Initially, he sets strict rules for himself regarding whom he should follow and for how long, but he soon discards them as he focuses on a well-groomed, handsome man in a dark suit. The man in the suit, having noticed he is being followed, quickly confronts the Young Man and introduces himself as "Cobb". Cobb reveals that he is a serial burglar and invites the Young Man (who tells Cobb his name is "Bill") to accompany him on various burglaries. The material gains from these crimes seem to be of secondary importance to Cobb. He takes pleasure in rifling through the personal items in his targets' flats and drinking their wine. He explains that his true passion is using the shock of robbery and violation of property to make his victims re-examine their lives. He sums up his attitude thus: "You take it away, and show them what they had."
The Young Man is thrilled by Cobb's lifestyle. He attempts break-ins of his own, as Cobb encourages and guides him. At Cobb's suggestion, he alters his appearance, cutting his hair short and wearing a dark suit. He assumes the name "Daniel Lloyd" based on the credit card Cobb gives to him and begins to pursue a relationship with a blonde woman whose flat he and Cobb burgled. The Blonde turns out to be the girlfriend of a small-time gangster (known only as the "Bald Guy") whom she broke up with after he murdered a man in her flat. Soon, the Blonde confides that the Bald Guy is blackmailing her with incriminating photographs. The Young Man breaks into the Bald Guy's safe, but is caught in the act by an unidentified man. He then bludgeons the man with a claw hammer and flees with the Bald Guy's money and photos. Upon returning to his flat, he finds that the photos are innocuous modeling shots.
Confronting the Blonde, the Young Man learns that she and Cobb have been working together to manipulate him into mimicking Cobb's burglary methods. She tells him that Cobb had recently discovered a murdered woman's body during one of his burglaries and is attempting to deflect suspicion from himself by making it appear as though multiple burglars share his MO.
The Young Man leaves to turn himself in to the police. The Blonde reports her success to Cobb, who then reveals that he actually works for the Bald Guy. The story about the murdered woman was part of a plot to deceive both the Blonde and the Young Man: The Blonde has been blackmailing the Bald Guy with evidence from the murder he committed in her flat, and he wants her murdered in such a way that it cannot be connected to him. Cobb bludgeons the Blonde to death with the same claw hammer that the Young Man used during the burglary of the Bald Guy's safe and leaves it at the scene. The police, checking out the Young Man's story, find the Blonde murdered and the claw hammer with his fingerprints on it. The Young Man is thus implicated for the murder of the blonde woman. Cobb, meanwhile, vanishes into a crowd.

Question: What is the bald guy blackmailing the blonde with?
Answer: Photographs