There are two enhancements coming to the Background features in Teams soon.
Admin Controls:When background images became available in Teams, there were no admin controls for the feature. Soon there will be a new meeting policy to control this feature. This policy will be available through the "SkypeOnlineModule" in powershell. According to the Message in the admin center, this is the syntax for changes, on a per user basis:
- Grant-CsTeamsMeetingPolicy -Identity "email address" -PolicyName "BlurOnly"
Interestingly, one of the settings in the above set of options "AllFilters" is described as: AllFilters, which includes the ability for users to upload custom images.
This feature, coming by the end of May will give the users an official way to add custom images within Teams.
If I understand the roadmap item correctly, the default will be "AllFilters"