Main Product Photos
"Image" > "Product Photos (Main)"'s recommended image size is 750 x 750 pixel, file type JPG or PNG, maximum 12 photos.
Additional Product Photos
"Info" > "Additional Product Photos"'s recommended image size is smaller than 2000 pixel and it will be resized to under 750pixel, up to 20 photos
For more information about uploading videos or images to product description section, please visit here