Currently at work we use Microsoft Teams and in teams you can set some background. But wouldnt it be nice to use a custom background that you like.

If you have the latest version there should be an option to select a background image. This means custom images can be added.

Windows

Save your image in the Uploads folder below:
C:\Users\<username>\AppData\Roaming\Microsoft\Teams\Backgrounds\Uploads

OSX

/users/<username>/Library/Application Support/Microsoft/Teams/Backgrounds/Uploads

Then, in teams while on a call; click the More Actions (Three Dots) at the bottom, select Show Background Effects
The pictures you added should show up on the right hand side of the screen with the default options from Microsoft.