You can mark usage types as applicable for high resolution images by checking the box "Is considered high resolution" when editing a usage type.
There is a setting in the application settings file at [tomcat]/webapps/asset-bank/WEB-INF/classes/ApplicationSettings.properties called 'image-size-considered-low-res'. If an original image's pixel area is less than the value of this setting then the asset will be considered low resolution and any usage types marked as high resolution will not be displayed on download.
For example if you set the setting at 100,000 an image which is 100x100 (10,000) will be considered 'low-res' so 'high-res' usage types will not be displayed. If however an image was 1000x1000 (1,000,000) then the image would be considered 'high-res' and 'high-res' usage types would be shown on the download page.
This setting only applies to images and does not apply to other file types.