The nemesis of Wall Street’s high-frequency traders operates out of an apartment-sized office above the Bliss Salon -- manicure/pedicure $45 -- on Elm Street in the Chicago suburb of Winnetka. Staring at four computer monitors,Eric Scott Hunsader, the founder of market-data provider Nanex LLC, looks for hints of illicit trading hidden in psychedelic images of triangles dancing with dots that represent quotes to buy and sell U.S. stocks broken down by the millisecond. Charts of trading produced by Hunsader’s eight-person firm have captivated everyone from regulators to art gallery owners. One stunt involved a computerized piano piece mimicking quotes for an exchange-traded fund. He infuriates some traders, who say Nanex draws unwarranted conclusions and spreads conspiracy theories. To Hunsader, the images created from market feeds are evidence of high-frequency trading firms exploiting market rules to turn a profit in a lawless environment. Though others in the industry see his reports and charts as propaganda, Nanex’s interpretations are helping to drive the public debate about the fundamental fairness of the modern stock market.