The flashes lasted too long to be gunfire. And the videotapes that the public saw on the evening news were copies that had been altered by an unidentified technician in some TV studio who probably added the sound of gunshots to make the broadcasts more exciting. Those were some of the dramatic and occasionally controversial conclusions of researchers who examined FBI surveillance videotapes taken at the Branch Davidian compound in Waco, Texas, on April 19, 1993. Nearly eight years to the day since 80 people died in the siege and subsequent fire at the complex on that date, a standing-room-only crowd packed a 300-person lecture hall at SPIE in Orlando, Fla., to hear a panel of four image analysts present their separate findings…