How did Google images normalize the width of each row?

Answer 1

Remember in google images (apart from cropping) -

1. Spacing between images are not always exactly same.
2. Height of all images in a row are also not always same.

Using above 2 techniques i.e. tweaking the spaces between images and changing size of image little bit by compromising height you can achieve this. In fact the the justify paragraph option in the text editor also use the spacing technique. They evenly distribute the extra spacing between all word.

You don't always get a good spacing in google image search. See this -

Answer 2

they actually figure it out through an algorithm to put images next to eachother so with the padding and everything they end up being the same width then they cache that page for the keyword you searched for!