Send any camera's image to any picture frame or media player

I’d like to add functionality to take a camera entity’s image upon a trigger (door bell ring for example), and send it to media_players or picture frames that can display it. I’d like to do this in a generic way using homeassistant internals, not custom shell scripts.

a) what’s the way to programmatically access the still image entity from a camera, for example my doorbird?

b) what’s a good way to make a component for a media player or picture frame expose a service call that can take this internal entity image? For example, can you send an image to a chromecast? I’d also like to send it to my Meural picture frame, which in essence has a REST API and one method through which to POST an image.

First, you can take a snapshot from your camera device https://www.home-assistant.io/integrations/camera/#service-snapshot

But you may be better with the play stream service https://www.home-assistant.io/integrations/camera/#service-play_stream