What is the best protocol for uploading images in batch via FTP? What is the best protocol for uploading images in batch via FTP?

Let's say my website has 3 images.

Original size is 1000x1000

I upload all images via backend as "image upload".

Later on, I want to substitute all 1000x1000 images with identical images with same name but at size 400x400.

Curious as to what is the best workflow for Drupal for this scenario.
I want to substitute all 1000x1000 images with identical images
  with same name but at size 400x400.


Since they are identical, simply use image styles. Create an image style of 400x400 and assign it to your content type's image field OR in your image field settings in a View.

Watch: How to apply image styles in Drupal