How can I print article author profile picture?
Put this on top of your node.html.twig or similar template

{% 
  set author_pic = {
    '#theme':      'image_style',
    '#style_name': 'thumbnail',
    '#uri':        node.uid.entity.user_picture.entity.uri.value,
    '#attributes': { class: 'authorImg' },
  } 
%}


Use this anywhere in the same template you want to output the author image   

{{ author_pic }}