Steven Powell, 61, was arrested at his Puyallup, Wash., home and set for arraignment Friday in Superior Court.
Prosecutor Mark Lindquist said Powell was charged with 14 felony counts of voyeurism and one count of possession of child pornography. He said police found "thousands of images of females being videotaped without their knowledge, including Susan Powell," on tapes and discs seized from his home during an Aug. 25 search as part of their investigation into her disappearance.
Powell is the father of Josh Powell, Susan's husband, who is the only named person of interest in his wife's disappearance. Josh Powell has never been arrested or charged in the case. The two live together in Washington.
"The photographer focuses on the women's buttocks, breasts," Lindquist said in a statement. "Many images were of minor females."
The images included shots of two girls who were as young as 8 and 10 years old at the time, the prosecutor said.
Pierce County authorities determined those girls lived near Steven Powell from June 2006 to August 2007.
A person who answered the phone at the Powell home Thursday night hung up on a reporter.
In a statement issued late Wednesday, West Valley City, Utah police, who are investigating Susan Powell's disappearance, said Steven Powell's arrest was not related to the missing persons case.
West Valley City police have said Josh Powell has been uncooperative in the investigation into his missing wife. He claims he took the couple's two sons -- then ages 4 and 2 -- on a midnight camping trip in the mountains west of Salt Lake City on Dec. 6, 2009, the night before Susan Powell was reported missing.
Authorities have spent the last 11 days searching a remote central Utah desert about 30 miles from where Josh Powell claims he went camping that night. At one point, they said they found a "shallow grave" after cadaver dogs alerted them to the spot, but they later found no human remains.
The search of the Powell's home came after police wrapped up a search for evidence in a network of abandoned mines outside Ely, Nev.
Around that time in August, Josh Powell and his father went on national television to discuss the case.
They claimed Susan Powell was promiscuous, emotionally unstable and suicidal, a claim her family denies.
Steven Powell said he had a flirtatious relationship with his daughter-in-law and believed they were in love.
"Susan was very sexual with me," Steve Powell told ABC's Good Morning America. "We interacted in a lot of sexual ways because Susan enjoys doing that."
Susan's father, Chuck Cox, denied the allegations, and said it was Steve Powell who initiated unwanted sexual advances. Cox didn't return a telephone call Thursday night.
Josh Powell has denied killing his wife or having anything to do with her disappearance.
"I would never even hurt her," a tearful, red-eyed Josh Powell told CBS' Early Show in August.
Josh and his father have said they believe Susan Powell ran off with another man.
"I'm still thinking she left," Steve Powell told the AP in August. "Hopefully they'll be able to find her at some point. ... We don't believe she's dead."