> For the complete documentation index, see [llms.txt](https://docs.tdmai.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.tdmai.org/metadata-binding.md).

# Metadata Binding

## Options for Binding Rightsholders' Preferences

When it comes to managing rightsholders' preferences for TDM in a machine-readable way, in principle, three different attachment mechanisms are discussed: 

1. **Location or domain-based metadata binding**: rightsholders' preferences for web-published content are included in robots.txt-file or in HTML/HTTP metadata of the domain, e.g. Robots.txt;
2. **Asset-based metadata binding**: provenance metadata – including rightsholders' preferences – is embedded directly into the media file, e.g. C2PA.org.
3. **Registry-based metadata binding**: ISCC fingerprints and preferences is submitted to publicly accessible registries. 

<figure><img src="/files/4ebnIPkX4XwocsMKXaAd" alt=""><figcaption></figcaption></figure>

## Why Do We Need Opt-Out Registries?

* Embedded metadata is removed from the media file.
* Content is altered or manipulated, compressed or converted into a different file format – which is where methods based on cryptographic hashing fail.
* When content is already distributed, shared and part of training sets, metadata cannot be embedded.
* Content is shared on websites beyond the rightsholder's control, e.g. on social media, so a domain-based approach cannot be applied.
* A lot of content is not publicly accessible on web domains.
* Watermarks or steganographic data can be removed from media files.