When displaying images on the list page of an e-commerce website, what methods are generally used to prevent image deformation?

I would like to ask, on a product list page similar to that of e-commerce, how do you generally prevent images from being deformed? Well, I looked at Tmall and JD.com and found that the original size ratio of the pictures is the same. Is it a unified rule for the size ratio of the pictures uploaded in the background?