A Marine spokesman said he could not comment on the continuing investigation.

The scandal has now spread to the Army and Navy, which are investigating similar photo sharing groups. But for the tens of thousands of women serving in the military, even successful prosecutions may have little effect on the minefield of bias they say they confront.

More than any other branch of the military, the Marine Corps has resisted integrating women. It still trains recruits separately and fails to give women properly fitting body armor, which the Army has provided for years.

“Almost every woman I know in the Marines has faced this kind of harassment, and you try to show you are tough enough to ignore it,” said Justine Elena, a former Marine captain who served in Afghanistan and now works for “The Daily Show.” “But at some point, by ignoring it, you just condone it.”

She recalled an instance when fellow Marines took photos of women in the bathrooms on a ship a friend was serving on.

“We need to stand up and say that is not what the Marines is about,” she said.

Last week, after hearing of the widespread photo sharing, Ms. Elena set up a fund-raiser called Female Marines United, in which people could show their opposition to Marines United by donating money to support mental health care for Marine veterans.

Ms. Cunningham, who is just a few weeks away from placing her feet on the painted yellow footprints at basic training that are the symbolic first step in becoming a Marine, said that while she had often been torn about how to respond to the online harassment, she had decided that the best response would be to become the best Marine possible.