Hi. I’ve moved your post to the Expo SDK category. I think it fits better there 
I think what you’re asking for is basically as follows:
You want the camera to capture a shot/frame, but instead of saving it to a file you want to get access to that (e.g. as a string).
My understanding of how React Native (and therefore Expo) works is that the camera hardware would be controlled by native code and for this data to be sent back to your JavaScript code it would need to be copied over the “bridge”. Copying large amounts of data over the bridge is slow, so that needs to be avoided as far as possible.
e.g. if an app needs to take a photograph and upload it to a server it’s better to get the native code to take a photo, save it to a file and return just the URL of the file to the JavaScript code. Then the JavaScript code can call into some more native code to upload that file. That way the actual file contents don’t need to be copied over the bridge.
In your case it seems that the actual data would need to be copied over the bridge. But if you give us more information about what you’re trying to accomplish, maybe there’s a way to avoid this.
Unfortunately I don’t believe Expo currently has a way to take the photo and somehow store/return it as a string/blob instead of saving it to a file.
Expo used to have some experimental AR functionality. Maybe something like that could be used for what you’re trying to do? If I were you I’d do some searching for info on “react native AR”.