Hi jc758
The images are normally included as a part of the teaser body. Therefore it's not possible to expose a rest call, simply because the teaser can really be anything - it's a text field that the user can populate with arbitrary HTML markup and it's not safe to assume that a teaser image will always be present in your code.
A potential improvement would be to include the image parsing logic in a Macro - so that you can define it once in the Endpoints section in Studio and maintain it in one place, then simply use the macro on the teaser content in your components which would greatly clean up your logic.
Hope this helps,