Clover [Genesis] - Recommended Image Sizes
Featured Image Size
For your featured images, images must be at least 800x1050px, but no larger than 2400x2400px. This size will ensure your images display correctly in all areas of the theme (front page, blog page, category pages, etc).
Post Carousel
If using the Post Carousel widget shown in the Blog demo, your featured images must be at least 1200x1050px.
Post Image Size
The width of the blog post column is 815px. For the clearest possible display, we recommend uploading images roughly twice that size (1600px is good).
If page speed is a concern, you can upload images right at 815px, but your images will be fuzzy on retina devices. Larger images don't affect pagespeed all that much, unless you have a large number of images in each post.
If you're using the full width post layout, the post column is 950px and images should be at least that size.