how to make images change on scroll up and down

Hi, I have seen on several sites the ability to change the image when you scroll down and up for instance the top image on a page that when you scroll down and then back up to the top has changed. Here is an example:https://chubbysjamaican.com

Thanks in advance!

Hi Creedon, initially I had thought it was a clever bit of coding but yes its just a slide show...I never stayed on the image long enough to realize! So I implemented the same thing and yes when I scroll up and down it appears to have different images. Obvious now! and thank you very much for taking time to have a look! much appreciated!

https://georgianbaysurfclub.squarespace.com/apparel-1