Market - Image Sizes
740px / 1480px
Your blog posts are sized at 740px in width. I generally recommend that your images have a minimum width of 700 pixels, with images ideally uploaded at 1480px in width to ensure they look clear on Retina displays. If you're not sure if your users access your site on a Retina display, know that recent releases of Apple MacBooks and iMacs all have 5k Retina displays. However, the best way to tell is to install Google Analytics and check the stats related to Browser Settings. There you'll be able to easily see what types of screens your users are viewing your site on.