The offence of voyeurism (section 162 of the Criminal Code) was enacted in 2005 to address public concerns with the rapid advent of technology that could be used to spy on people surreptitiously for sexual purposes.
“For a sexual purpose”
Subsection (b) of the offence specifically makes it an offence to surreptitiously observe or surreptitiously visually record a person who is nude. Subsection (c) requires only that the surreptitious observation or surreptitious recording be “done for a sexual purpose”.
Because observing or visually recording for a sexual purpose is a separate offence, it is clear that the voyeurism offence can be committed where the victims are not naked, but where the focus of the observation or videos is on sexual organs or where there are other indicia that the intent of the accused is for a sexual purpose.
R. v. Jarvis, 2017 ONCA 778, at para. 44; for more on what constitutes “for a sexual purpose” see R. v. Sharpe, 2001 SCC 2,  1 S.C.R. 45, at para. 50.
In R. v. Rudiger, 2010 BCPC 182 (CanLII), the circumstantial evidence pointing to a sexual purpose was compelling. The accused used a video camera to view and record very young children playing in a park, focusing in on their genital and buttocks regions. There was also evidence indicating that the accused was masturbating while doing so. The finding that the recording/observation had been done “for a sexual purpose” was not challenged on appeal.
In R. v. Jarvis, 2017 ONCA 778, a high school teacher used a camera pen to surreptitiously take videos of female students as he conversed with them at school. The Court of Appeal for Ontario (at para. 46) held that the recordings, which focused on the breasts of the teenaged female students, were “for a sexual purpose”.
But see R. v. Taylor, 2015 ONCJ 449, where the accused took pictures of women’s buttocks while they were sunbathing in thong bathing suits on a beach. When considering the sexual purpose component of the offence of voyeurism, the trial judge concluded that he could not discount the possibility that the pictures were taken for artistic reasons.