Two brothers accused of attempting to extort money from jockey Gary Stevens pleaded not guilty to criminal charges Wednesday in Los Angeles Superior Court.Mark Frankel, 25, of Sherman Oaks, Calif., and his 29-year-old brother, Adam Frankel of Encino have been charged with extortion and conspiracy. They are free on $35,000 bail. Their next scheduled court hearing is Feb. 26.Authorities said the two men allegedly tried to get Stevens, 37, to pay them $200,000 last month in exchange for a set of photos of the jockey moments after the 1995 Kentucky Derby. The snapshots -- reportedly taken from ABC television stills -- show Stevens giving a high-five to fellow jock Pat Day. Police said the two brothers believed the photos show Stevens passing an illegal electrical device to Day.After a series of phone calls and planned drop-offs between Stevens and the Frankels with police officers listening and watching, the two men were finally arrested on Dec. 21. Police believe a third person may have been involved in the extortion scheme.Authorities aren't sure why Stevens was targeted and don't believe the Frankels knew the jockey.