How to shrink all <img> pictures on a webpage to 60% or original width/height?

How to shrink all <img> pictures on a webpage to 60% or original width/height?

Assume I have the following webpage:

https://www.raymond.cc/blog/5-system-rescue-boot-disc-based-on-windows-pe/

After loading the web page in Firefox I want to execute a jQuery script which shrinks all images (of the core article) to 60% of the original size.

jQuery script execution should be triggered out of a Greasemonkey script.

So how would a jQuery statement look like which selects all <img> elements, find out their original size, calculates the new size (without fraction) and applies the new width() and height()

Possibly one has to wait for 5 seconds until all images are successfully retrieved from server.

Thank you
Peter