SEO plugin question

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1

I’m using the SEO plugin to add all the header stuff. At the end of the docs it talks about setting up the image. It gives an example of 100*100. Is that the standard size for the “social” images or is there a range?

Edit:
I added:

defaults:
  - scope:
    path: ""
    values:
      image: /images/social/my-logo.png

to the_config.yml and I got an “undefined method ‘key?’ for nil:NilClass” and it could not read any of the posts. I’m using Jekyll v3.4.0 if that matters.