When the Yahoo! Store software needs to re-size the images you've upload to your store, these images are automatically converted to the format specified in the Uploaded-img-default-type variable field (GIF, JPG or PNG). If you do not specify a file format, resized images will be saved in GIF format with an 8 bit color depth.

The maximum size of your images is controlled by the various height and width properties in the Image Dimensions category of your Variables page. If you adjust the appropriate height and width values so that they are larger than or equal to the original uploaded size of your images, then the Yahoo! Store software will not need to re-size your images and this automatic conversion will not occur.