Swimming coach Craig Brown, 31, admitted using his iPhone to covertly take pictures and make videos of unsuspecting women in at least five locations.
Police discovered hundreds of images he had recorded at places where he was supposed to be working for Dundee City Council over a two-year period.
Mr Brown was caught when a swimmer spotted his phone under her cubicle door when he was working as a fitness coach at Perth leisure pool.
He admitted filming himself performing a sex act at the side of a Dundee high school pool and sending the video to a woman in the US.
A jury was told a major investigation took place into Mr Brown's activities across Fife, Perth and Kinross, Dundee and Angus.
Pools and schools where he was known to have worked were studied to see if they matched the backgrounds on the images found on his phone. A caravan park, three Dundee high schools and Perth Leisure Pool all featured.
Mr Brown - who used the term "voyeuristic" when searching for porn - admitted taking all of the footage but pled not guilty, denying it was to satisfy his sexual interest.
He said he did it to justify how bad he felt about himself. He said had not watched the videos and he had deleted them. He also denied posting them on the internet.
Mr Brown admitted he had been working as a swimming instructor between 2005 and 2012 and accepted he acted in a criminal manner by filming females.
He said he was not interested in looking at the videos, but the jury was told he had used "voyeur" as a search term in both his phone and his home computer. More than 1000 secretly filmed pictures, downloaded from the web, were found on his computer.
Police forensic computer expert Kevin Alexander told the jury he found a large collection of voyeurism pornography on Mr Brown's computer equipment.
Mr Brown admitted to the jury he was at Craigie High School in Dundee shortly before 8am on May 24, 2011, when he filmed himself at the poolside.
The video, sent to a woman in the US, was studied and police identified the location.
Mr Brown said he was supposed to be cleaning the pool at the time.
A lengthy joint minute was read to the jury in which Mr Brown admitted causing "distress" to numerous women by secretly filming them as they got changed. He was caught on February 7 when a woman realised she was being filmed, dragged Mr Brown out of the adjacent cubicle and forced him to hand over his phone.
He was reported to management at Perth Leisure Pool, arrested and then sacked from his post.
The trial continues. Mr Brown denies eight charges relating to covert filming of women in changing rooms between April 26, 2010, and February 8, 2012. The locations were Craigie, Menzieshill and St John's RC High Schools in Dundee, Perth Leisure Pool and the Red Lion Caravan Park in Arbroath.