Retro images have a margin on the bottom and right sides

The image generated with the default=retro option have a margin or internal border of some sort:

Example:

https://www.libravatar.org/avatar/13294c5d1d80d103b665a3596a7ed975e75e356b5b6af178eaf097b7c3130bf3?s=60&forcedefault=y&default=retro

Attached here: