Let's say I have my GitHub profile pulled up in the browser.
https://github.com/jbranchaud
If I then add .png to the end of that in the URL bar:
https://github.com/jbranchaud.png
I'll be redirected to the URL where the full image file lives. In my case:
https://avatars.githubusercontent.com/u/694063?v=4
You can pull up yours https://github.com/<username>.png to access your profile
image.