以下是官网的描述:
1、Rich in detail, e.g., street scene, group of people, collages and mixtures of items, sport scenes
2、Good contrast, i.e., bright and dark regions, well-lit
3、No repetitive patterns, i.e., a grassy field, the façade of modern house with identical windows, a checkerboard
4、Must be 8- or 24-bit PNG and JPG formats; less than 2 MB in size; JPGs must be RGB or greyscale (no CMYK)