How to show all content type images in a gallery
Follow below steps to resolve your issue.


Create a new view of type files.
Add Filter File:Mime Type and select the condition as Contains any word.
Give all image extensions in the value like jpeg jpg png etc
Rewrite the results of the File Path field and add img tag with src as file path.


Using above instructions you can list all images in Drupal independent of any content type or image field.