What does the '=s0' at the end of images on Google mean?

[toxicmix]

Hello guys.

Does anyone know what that "=s0" at the end of Google images is?

It appears on images published from Google contributors.

Insert CODE, HTML, or PHP:

photo-url/AF1QipM8MK78Zf1FeVcgVXaskfukcqqJkA5KOSnp9TYa=s0

Any idea what this is about?

Thank you.