Q: Other people's photo in my photostream

Did you at any point activate Photo Stream sharing?

http://www.imore.com/how-use-photo-stream-and-icloud-photo-sharing-ultimate-guid e

Yes, it has always been active.

daddydool wrote:

Yes, it has always been active.

That's likely why. Others are able to add photos to your iCloud Photo Sharing. Turn Sharing to OFF

iCloud Photo Sharing - Apple Support

I have been using sharing to share with my friends and family. This person is a total stranger and in the past 3 days I have received over 190 pictures. I checked all the invited names and I know everyone. Plus I frequently use the sharing option.

It sounds like an iCloud security issue to me. Might be best to talk with them.

https://www.apple.com/support/icloud/contact/

Ok, thank you.

You are welcome.