You should be able to share photos and other files from UWP apps directly into teams. For instance, if I run the "Photos" UWP application and click on "Share", "Teams" is not one of the possible options for sharing.
This ^^^. I simply want to share a photo as well to Teams using what was originally the share charms that were in Windows 8. Clicking the Share button in photos as an example, should bring up a list of apps to share with and Teams should be one of theses