When the list view is drawn, it must provide enough room for the images associated with each item. The size of the images used is specified by the ImageSize property of the list view field. If this property is set to System, large images are scaled to 32 by 32 pixels. Small images are scaled to 16 by 16 pixels. If the ImageSize property is set to First Image, all large images are scaled to the size of the first large image you define for the list view field. Likewise, all small images are scaled to the size of the first small image.
If you use the System setting for the ImageSize property, we recommend that your large images be 32 by 32 pixels. The small images should 16 by 16 pixels. Your images will then have the best appearance because they won’t have to be scaled. If you allow the image sizes to be based on the first image, we recommend that all the large images be a uniform size. All small images should also be a uniform size.
If you don’t supply both the small and large images, the image supplied will scaled to the proper size and used in place of the missing image.