Working with Images in Wordpress

Image sizes
  https://wordpress.org/support/topic/thumbnail-placeholder-resize
  https://wordpress.org/support/topic/changing-size-of-thumbnails-on-home-page
  https://wordpress.org/support/topic/thumbnails-on-galleries-are-in-different-sizes
  http://stackoverflow.com/questions/15685666/changing-image-sizes-proportionally-using-css
  https://wordpress.org/support/topic/i-beg-anyone-for-help-with-feature-post-image-dimension
  https://wordpress.org/support/topic/featured-images-not-properly-scaled
  https://wordpress.org/support/topic/resizing-thumbnail-sizes-to-smaller-using-child-theme
  https://wordpress.org/support/topic/post-thumbnails-20
  https://wordpress.org/support/topic/serve-scaled-images-optimization
  https://wordpress.org/support/topic/?replies=11\
  https://wordpress.org/support/topic/featured-image-resize-4

How to crop/size images
  http://havecamerawilltravel.com/photographer/wordpress-thumbnail-crop
  http://havecamerawilltravel.com/photographer/wordpress-resize-thumbnails
  http://www.davidtan.org/wordpress-hard-crop-vs-soft-crop-difference-comparison-example/
  http://www.wpexplorer.com/wordpress-image-crop-sizes/
  http://www.wpbeginner.com/wp-tutorials/how-to-create-additional-image-sizes-in-wordpress/

Cropping images
  https://wordpress.org/plugins/manual-image-crop/
  https://wordpress.org/plugins/post-thumbnail-editor/

Responsive Images
  http://blog.cloudfour.com/responsive-images-101-definitions/