I think I see the problem. When I add a landscape image it is blurry but when I crop to portrait it is okay, weird?

What is black overflow?

It is some of my images on the main page. If you hover over the kids blue hoodie towel you'll see what I mean.carterandmae.com.au 

https://carterandmae.com.au/

I have tried to resize my images to 2048 x 2048px at 72dpi. They are a little better but still blurry. It isn't every image so I've tried to imitate the ones that are clear and this doesn't work. I have also tried to change the code as suggested in o...