I was skimming the "Stack Exchange Network Terms of Service" until I came across:
Profile Content that is available via the Stack Exchange API ("API Profile Content") is perpetually and irrevocably licensed to Stack Exchange and its Subscribers under the Creative Commons Attribution Share Alike license
Profile Content that is NOT available via the Stack Exchange API ("Personal Profile Content") cannot be used for any commercial purpose, individually or in aggregate, or be republished without the explicit consent of the author of such Personal Profile Content or the explicit consent of Stack Exchange.
The thing is that I found my profile picture I use in StackExchange.com websites online from a website claiming it is in public domain. Now I am wondering if I have unintentionally licensed this public domain image to StackExchange Inc. or myself? In other words does the image on the source website stay in the public domain?
Note: I have cropped the image to use in my profile.