Need to add image through php code

Dropbox does offer an API you can use for listing, uploading, downloading, and sharing files, among other operations. You can find everything you need to get started with the Dropbox API, including documentation and tutorials here.

For example, to upload files you can use /2/files/upload, and to create shared links you can use /2/sharing/create_shared_link_with_settings.

For reference, Dropbox doesn't offer an official PHP SDK for Dropbox API v2, but you can use a third party library, or you can call the HTTPS endpoints themselves using whatever HTTPS client you prefer.