How do I uplaod files?

Sorry to bother you with this, but I haven't had an easy time wrapping my head around it on my own.

I'm using Angular, and the frontend and the backend communicate through API only. This API has a method for posting an image, and that method returns the URL of the image posted. We use amazon web services for storing the images, but all the frontend needs to know is that it posts the URL through a POST HTTP-call and receives a json-document containing the url of the newly posted image (this response could be edited to only contain the url if this is needed for integration).

We are using the enhanced image functionality/plugin. The ability to add captions to the images is very important to us.

I'm wondering if any of you know how I should go about doing this?

Is there any easy way to configure how images are uploaded that in a way that enables one to use our own POST-call and insert the URL that's returned?

Is there a relevant plugin that will do this for me, or enable me to this with the help of configuring or some easy method?

Or is there some easier way to help us achieve what we want? (The ability for users to easily and intuitively add images to their texts, from files on their computers or urls already present on the web, and add captions the these images, without storing the images added from computer files in base64-format directly in the text.)

Any help would be greatly appreciated! :)