Below is a sample of the different sizes and ratio for product images. 

Different product types may require different product photography. Fashion generally works well with portrait 1000 x 1500 while jewellery usually uses a square ratio. 

Photos should be optimised for web, 72 dpi with 90% quality. 
For SEO purpose, we recommend you rename your files so your images can be found on Google image search. 
i.s - brandname_storename_productname_colour_size.jpeg