Joe Hatcher, who served in Iraq, Ryan Walker and Mali Eno joined a protest at a Colorado Springs-area Army, Navy and Air Force recruitment center in November.
The three are charged with trespassing, a misdemeanor, after they were accused of getting on the roof of the building and unfurling a banner that said, "End the War or We Will Start Our Own."
But the defendants say they were not responsible for the banner.
"I was on television being interviewed when the banner was unfurled," said Hatcher, 25.
"It's profiling and harassment. The only witness statement the prosecution has was written a month after the protest by an undercover vice officer."
Hatcher, 25, enlisted in 2000 and served in an Army reconnaissance unit in Iraq from February 2004 to March 2005. He plans to start college in the fall.
"We weren't on the roof and we have proof," said Walker, 20, who now works as a maintenance man in Colorado Springs. "The pictures (taken by other protesters) show us in the crowd the whole time."
Walker said that he, Eno, 22, and Hatcher have talked with attorneys, but will represent themselves, using photographs as evidence to support their position.
Ron Claeys, of the city attorney's office, said the prosecutor in the case, Victoria Ringler, is aware of the photographs.
"It's our burden to prove they were on the roof and we will have several witnesses," he said.
Claeys said several witnesses have been subpoenaed for the trial, which is expected to end by the afternoon.
Colorado Springs anti-war activists, including members of Iraq Veterans Against the War, have held counter-recruitment protests at schools for more than a year to give teens another point of view on military service and the war.
Walker said that about 20 protesters gathered outside the recruitment office in November, made statements and drew outlines of bodies on the ground to symbolize soldiers who have died in Iraq.
"The police asked us to leave. We were going to our cars when the cops cut us off and detained the three of us," he said.
He said the officers brought a witness to the parking lot and asked if the three were on the roof.
"He said we were the ones. It wasn't any kind of an official lineup," Walker said. "They took us in and charged us with trespassing."