Images generally should be uploaded to Hits in a Box as jpegs with a resolution of 72 ppi and a size of at least 1,000 pixels in width. The Image Manager also accepts .gif, .png and other image formats.
Images of a smaller size (say, 300 pixels) will be of extremely poor quality when viewed on devices with large screens. Images of a much larger size (say, 6,000 pixels) will not result in a higher-quality image and have the potential to affect page load times.
Shoot for a width of somewhere between 1,500 and 2,400 pixels.