Currently, the PayPal Catalog widget only allows for one picture per product. I can understand how you would like to have more than one image displayed for a product. There is a workaround but it requires you creating your own PayPal button for each item. Instructions for making your own PayPal buttons can be found here.
You can put multiple images of your product on your page in whatever format you would like, and then put the HTML widget with the PayPal button by your product.
Alternatively, you may want to consider using the Online Store which enables you to add multiple pictures!