Image copyright Green Party of Canada Image caption The original photo on the left shows Elizabeth May holding a compostable cup and the edited image on the right shows her holding a plastic reusable cup

Canada's Green Party has admitted to doctoring a photo of its leader to show her holding a reusable plastic cup.

However, leader Elizabeth May said the manipulation was done without her knowledge and she was "completely shocked" to see it.

The edited photo showed Ms May holding a plastic reusable cup with the Green Party logo and a metal straw.

The party leader said that she had nothing to hide as she was using a compostable disposable cup.

"My personal daily practice is to avoid single use plastic items 100% of the time," Ms May said in a statement.

"I walk the talk every day. I hope that despite this misstep by well-meaning party staff (who hoped to brand the image with our logo), people can believe that in the original photo there is nothing I would have hidden," she added.

The Green Party has committed itself to reducing plastic waste, including a ban on single-use plastics.

Canadians go to the polls on 21 October in what will be Ms May's fourth general election.