Images

Example with CKEditor WYSIWYG inline images field.

Also see : Create a Form with Drupal 8 using Form API

You can use IMCE to select a file.

Crop images using convert (ImageMagick)

Example (Single file):
convert input.jpg -crop 1300x950+312+72 crop.jpg
convert input.jpg -crop 1300x950-100-50 crop.jpg

Example 1, with FieldPluginBase (\Drupal\views\Plugin\views\field\FieldPluginBase)

Get the image file src (url)   
    $fid = 1;//The file ID   
    $file = \Drupal\file\Entity\File::load($fid);
    $path = $file->getFileUri();
    $url = $file->createFileUrl();
    OR
    $path = 'public://images/image.jpg';


Inlinux debian / ubuntu / mint ...

1. Install imagemagick tools (if not installed)
# sudo apt-get install imagemagick

2. Process images like : (here resize images to 50%)
$ for i in $( ls *.jpg); do convert -resize 50% $i re_$i; done