I think if you have uploaded your category image and designated it on the category page and have uploaded a different image(s) to the product page everything will work fine when you change the item to In Stock instead of Sold Out. Whenever a customer views a page where the item is not available for purchase or an empty shopping cart there's a setting in Admin under Stock that you can turn on or off that shows the New Products listings.

Those "additional images" you are seeing is the New Products page. If you add quantity to an item then the Sold Out button should be replaced with Add To Cart and the Product image and additional images will be shown when viewing the Product page and the New Products page won't show up any more.