General Image Advice
Image Size
In days past, it was common to have images with certain size requirements. With modern web design, websites are
responsive, which means they are meant to look good on any device size/shape. With responsive design, there is not a specific size to use for images because they will be resized and repositioned as you view your site on different viewports.
To maintain good quality, however, as a general rule, we recommend uploading images that are at least 1800 pixels in width. This will ensure a quality image in most any website context. The system will size down the image and compress it for efficiency if it is used in a smaller context, or keep it large and uncompressed for larger contexts, so you don’t need to worry much about sizing.
Image Shape
More important than the size of the image is the shape. It is often ignored, and this creates some undesirable results. For instance, if you are trying to create a banner image in a horizontally-oriented page header, and you use a tall, vertically oriented picture, it will probably end up in a lot of cropping and the image won't look as good as might be desired. Therefore, try to pick images that are close to the shape of the area where you want to use them.