How do I put photos uploaded to my website in a grid like form?

For example, my website offers different sizes for the photos uploaded. One size is a perfect square, another size is portrait, and the other is landscape and i would like to fit all the photos on my website with equal spacing between all. I would like to do it the same way flickr organized their photos when you search something or pinterest. All i could do is manually put different margin spacing in the css of each photos but that will never work when my website is up and people start uploading photos on their own. So how could I do this