Let's say you don't like some of the default icons in Confluence, like the one for the anonymous user:

And you would like to use something livelier, like a picture of a Lhasa Apso puppy:

To replace all you need to do is the following:

1. Shutdown Confluence
2. Navigate to <Confluence Install>\confluence\images\icons\profilepics
3. There you will see an image file named anonymous.png (this is the image that represents the anonymous user icon)
4. Backup the image
5. Open anonymous.png with an image editor so that you can find the image dimensions. In this case, the dimensions of the anonymous user icon is  "48x48"

6. Now edit the image you want to use instead and make sure that this image has the same dimensions as the icon you're replacing

   You can use an online image re-sizer like http://www.picresize.com/ to change the file dimensions

7. After you replace the file, start Confluence

8. Enjoy!
   

Notes

• In case you notice any misbehavior regarding your new icon, shutdown Confluence and restore the image you backed up previously.
• When you upgrade Confluence, you will need to migrate your custom icons to the new installation directory (<Confluence Install>\confluence\images\icons\profilepics).
• In case you want to edit other icons you can check the files at <Confluence Install>\confluence\images\icons. Be sure to replace the existing file with a new file using the same name.type.