Plugin not displayed on an article

I paste the shortcode inside an article in joomla 3.4.8 like this:
{twenty}image1=path_to_the_image1|image2=path_to_the_image2{twenty}

Obviously replacing the path_to_the_image1, for the right image path, but it haven't displayed, I did make sure that the plugin was on in the plugin manager.

Can anybody helps? thanks