Symptoms

Set a profile picture of yourself. Go to any page added by other user, hover onto the user's username and you can see the user's profile picture. This behavior is correct and expected. Click on the profile picture and you'll be redirected to the user's full profile page. On the page however, you'll see that the user's profile picture is replaced by your own profile picture instead. 

Diagnosis

Check on these areas of customizations:

1. Confluence Admin >> Layouts - Backup all custom layouts and reset them to default

2. Confluence Admin >> Custom HTML - Backup any custom HTML and reset it to default

Cause

Custom layout customization has caused this problem

Resolution

Reset the layout setting to default.

Admin can also re-assess the customization made onto the layout and find out which line of code was causing the problem and remove it. Note: Layout customization falls out of Atlassian Support Scope.