Are there recommended sizes for images for thumbnails, the mail image and the enlarged image?
The sizes that you select will depend largely on the layout and design of your store, as well as the type of products you are selling and the shape of the images.
Using our scaling tool in your Order Management System, try scaling the thumbnails to about 150 pixels wide, the main images to about 250 pixels wide, and the large images to about 400 pixels wide. See how that looks in your online store, and you can play with it up and down from there. Once you've decided on what will look best in your store, you can re-size the images accordingly either in Photoshop or some other image re-sizer, or by using our resizing function in the OMS.
For the best-looking results, as well as the most optimally functioning store, be sure that all of your thumbnails are the same size, all of your main images are the same size, and all of your large images are the same size (and if you are using the image gallery, that all of your mini-thumbnails are the same size)