I want to get all the images from /_layouts/15/images/

Hello,

The server directory may not be accessable for SharePoint Online. Also I happen to have a test on prem enviorment in Azure so I took a look at the folder you were looking for and found it here instead: C:\Program Files\Common Files\microsoft shared\Web Server Extensions\15\TEMPLATE\IMAGES

This is a server directory and can not be accessed though the URL in the browser.

Anyway I discovered there are 3128 images in this directory. I tried to Zip them up and attach them but the one zip file exceeded the file size upload limit for this site. I'll split it up into two zip folders for you.

Have fun,

Chris.