Images are, well, images! Buttondown allows you to upload images to its secure S3 bucket and do with them what you will. This is sort of an odd duck of an API, to be sure, but if you want to be able to do things like draft and send emails completely on your iPad you need a surefire way of creating images.
A unique TypeID associated with the object.
The date and time at which the object was first created.
The URL of the image.
A structured key-value blob that you can use to store arbitrary data on the object. Metadata can be nested — you can store objects and arrays within your metadata. (You can read more about metadata.)