On the "Product" tab you can enter a product image to showcase it.
You can enter either the image file name or a complete URL of an online image in the "Product image" field on the Product tab.
To upload your own image, follow the "Using the upload function" page of the "Managing your website" section of the Help files.
The target directory for your image is ../public/storemaker/images
The image can be any image format (gif, jpg, bmp, etc.)
To use a current online image, enter the complete URL of the image.