When uploading a png profile photo that has a transparent background, the default avatar icon is seen behind the photo. This only affects the Plex web and Plex for windows players as far as I can test. Other places where the profile photo appears do not have an avatar background.
Examples of the avatar background:
Photo Area under Account
Top Right of Web and Windows Application
Examples of no avatar background:
Plex Website
Plex on Android
Furthermore, the Xbox One Plex app has a really buggy and pixelated profile photo when using a transparent background. I am on the early access version, but thought I’d mention it anyway.
Here’s what it looks like:
