The party is conducting a contest to make fun of Harper's stance on global climate change initiatives, the Canwest News Service reported. One photo submission featured Harper's face superimposed on that of Lee Harvey Oswald being gunned down by Jack Ruby after Oswald's arrest for allegedly shooting U.S. President John Kennedy in 1963.
Liberal party spokesman Daniel Lauzon told Canwest in an e-mail the picture only appeared on the Web site briefly before being taken down.
"Though we do screen the pictures before posting them, it appears the Lee Harvey Oswald picture slipped through the cracks -- it has since been removed," he said. "We apologize to those who took offense to the image."
Lauzon acknowledged another modified photo showing Harper with his hand up a cow's rear end had also been removed from the Web site.
"It was considered a joke on methane emissions from cattle. But since it can be misinterpreted, it was taken down as well," Lauzon said.
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'
Toddler uninjured after being knocked over by Obama family dog