This image below is 100 pixels wide and 67 pixels tall. The aspect ratio is correct at 3:2. The entire image is displayed in the image preview above. However, because the overall image size is so small, the image has to be stretched to fill the space, so it doesn't display as clearly and crisply as it would at higher resolution.
Images should be at least 800 pixels wide and 533 pixels tall. They may be larger, but for the best display, they should not be smaller.