the music box
SPOILER
It's hard to credit that the blackmailer would keep his 'meal ticket' (the damning photographs) still hidden inside the music box when circumstances forced him to hock the item. Take note of how quickly and easily Jessica Lange's character found them virtually within seconds. It would have stood to reason that the pawnborker's staff would have glanced at the box, if not out of curiousity at such a unique item, then to estimate it's possible value.
Common sense would dictate that the photographs would have been removed and safely stashed somehwere else.