Customize the system-comment-avatar from an icon of a 'grey head' into a custom image

Hello 😄

I was wondering if the following is possible:

See this image below? https://assets.squarespace.com/universal/images-v6/default-avatar .png

That's the default image that we see on a Squarespace website when someone, who doesn't have an account and isn't logged in (like in my case, most people), leaves a comment under a blog post.

 I'd like to use a custom image instead of the boring grey image, but am not sure if this is possible. Can it be done with some custom CSS?

Preferably, I'd like to show a different default avatar.png.
Can it, for instance, link to another image that I've uploaded instead? Like the one below? (This is just an example image for the time being, but was uploaded to my website)
For instance: this one: https://images.squarespace-cdn.com/content/v1/5ea2ece99c62cc1c1c322a6c/7c37ccfb-228f-474b-9c74-cbe302793a4b/avatar-comments.png 

I'm curious if it's possible. So far I haven't seen anyone else asking this specific thing yet.


Thanks in advance for having a look at my request.
Have a great day!

Best,

M. 

Can you share link to a blog post with some comments? We can check problem easier.