Every user profile gets an auto-generated picture by default: a pattern image made from the account id. It is the same everywhere your account appears, in comments, reviews, verdicts and lists.
Users cannot upload their own photo. A profile picture should show the real person behind the account, so an arbitrary uploaded image is not accepted.
To show a human photo, your user profile (/user/@name) must be connected to a human profile (/human/Name), the article about you as a real person. The connection has to pass moderation, so that nobody can take the photo of someone else. Once it is approved, your user profile shows the photo of that human profile.
Until the connection is approved, the generated picture stays. Use the info icon next to the picture on the settings page to open this page.