Hello,
how can I change the image style used for user profile pictures in comments and created nodes?
For me, they are always displayed in their original size. I would like to use an image style like "100x100 pixels," for example.
Sample from this Forum:

In nodes it is quite easy. Go to the Admin menu:
Admin Bar > Structure > Content types > Post (as an example) > Manage displays > Default
You can then select the Image style you want for the image field.
In comments it is not as obvious but you need to go back to the User Account Settings
Admin Bar > Configuration > User accounts > Account settings
You can then choose the image style