The graphic color photo, flashed on a large video-screen stationed next to the jury, tested the decorum of a federal courtroom.

It showed a nude woman named Rona tethered to a tree trunk in the wilderness. From the witness stand, Rona answered questions about the bondage scene in graphic detail, casually complaining that her body was bitten up by mosquitoes.

The testimony came during a sex abuse trial in Brooklyn that has given jurors lessons on the lifestyle of a man dubbed an “S &M Svengali” by the tabloids, the inner-workings of the sadomasochism underground and the federal government’s crackdown on obscenity.

The jury was expected to begin deliberating today.

In recent years, federal authorities have stepped up prosecutions of purveyors of hardcore adult pornography to “protect citizens from unwanted exposure to obscene material,” Attorney General Alberto Gonzales has said. One pending case in Pittsburgh — involving videos of simulated rape and murder — was initially thrown out before being reinstated on appeal by the Department of Justice.

Under the Bush administration, at least 52 people or businesses have been convicted of violating federal obscenity statutes, and more than a dozen indictments are pending, federal officials said. By comparison, there were four such prosecutions during the eight years of the Clinton administration, they said.

In the Brooklyn case, Rona and the prosecution’s star witness, named Jodi, gave conflicting accounts of an alleged campaign of sadism by Glenn Marcus, 53, operator of a sex-themed Web site.