What is the recommended resolution for the Image in Stellar?

Stellar layout is bet fit for wide images. If you want to use square image, the classic layout will be the best choice. We can also enhance the image sizing and display by adding more height to the feature image container. Currently, it is 75% of the screen height which can be modified by adding following CSS snippet in Divi theme panel (change 75 to the higher number but under 100):

 .el-featured-image{
height: 75vh;
}