How to include multiple images of specific size to pages and posts

I wish to create a theme template file whereby a page can have 3 images attached to it of specific sizes.

One would be 500px by 300px and two would be 180px by 180px each.

I know how you would do this with just one as a Featured Image – but as far as I know you are only allowed one Featured Image per post or page?

I can’t do this with custom fields as I want the image to be “cropped” or “re-sized” by WordPress rather than by the user in Photoshop.