If you are uploading your images to your website, it is important to consider the size in both dimensions and file storage size – this is called optimizing your images for the net.
It is important to have your images at the recommended pixel size. If your image is too small, WordPress may stretch your image to fit to its given position on the page and this will result in a blurry image. If your image is too big, WordPress will use their resizing algorithm to reduce the size of the image to fit into the page which may display an image which isn’t as sharp as you would like, and may also serve up the big full-sized image in the background when the web page loads, leading to a slow loading time and a poor experience for the viewer – perhaps making them click away from your site in frustration.
How to resize for your website.