How to extract data from the iphone backup on the PC
Well, I´m not a pro-windows user here, but I do use some good old USB connection from my Iphone and my work computer using Autoplay


So, if you did save your images locally into your device, you should be able to get them from there !

Otherwise you should change the parameters of Whatsapp to save your image into your Photos and then try Autoplay.

As you said, it is as simple as connecting a USB cable between the two.