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ISCC - Specification

The ISCC is specified at two complementary levels. ISO 24138:2024 is the authoritative International Standard that fixes the normative core. The ISCC Enhancement Proposals (IEPs) are the open community specification process that documents the standard in detail and develops new functionality. The open-source reference implementation connects the two.

ISCC Standard - ISO 24138:2024

ISO 24138:2024 - International Standard Content Code (ISCC) is the authoritative specification of the ISCC.

ISO 24138:2024 - the International Standard

ISO 24138:2024 was developed under ISO/TC 46/SC 9/WG 18 and published on 15 May 2024 as the first-edition International Standard for the ISCC. It is the authoritative, normative specification.

The standard defines the ISCC as a multi-component, similarity-preserving code for digital content and specifies:

  • the ISCC-CODE structure - a self-describing header (MainType, SubType, Version, and Length) and a composite body assembled from one or more ISCC-UNITs;
  • the Meta-Code - similarity of the content's metadata;
  • the Content-Code - perceptual and structural content similarity, with per-modality algorithms for Text, Image, Audio, Video, and Mixed content;
  • the Data-Code - similarity of the raw bitstream;
  • the Instance-Code - exact data identity via a cryptographic checksum.

ISO 24138:2024 also carries a normative annex, Annex D, "Reference implementation". The reference software is published as a freely available electronic insert to the standard at https://standards.iso.org/iso/24138/ed-1/en/. It is normative in a precise sense: any conforming implementation, given the same conformant input, must produce the same output as the reference software. Implementations need not reuse its algorithms or programming techniques, and the reference software cannot add anything to the standard's textual technical description. The code of this electronic insert is maintained as the open-source iscc-core library.

Enhancing the standard - the ISCC Enhancement Proposals

ISO 24138:2024 is a complete working specification, and future editions are expected to add functionality, track the state of the art, address security concerns, and retire deprecated features. Annex C of the standard names the channel for this work:

A process to structure and substantiate proposals to enhance ISCC is maintained by the ISCC community. […] The ISCC community is gathering ISCC enhancement proposals at https://github.com/iscc/iscc-ieps.

The ISCC Enhancement Proposals (IEPs) are design documents that describe a feature of the ISCC system or provide information about its processes and environment. They are the detailed, openly developed working specifications of the ISCC community, and the route through which new work is substantiated before it can feed into a future edition of the standard.

How the IEP process works

The process is itself defined in an IEP (IEP-0000). In outline:

  1. Idea and discussion - a champion develops the idea and fosters public discussion.
  2. Draft submission - the proposal is submitted as a pull request to iscc/iscc-ieps.
  3. Editor review and numbering - an editor assigns a number and category and checks that the proposal is sound, complete, and motivated.
  4. Iteration - the author refines the draft through further pull requests.

IEPs are categorized as Core (changes affecting most implementations; require both a design document and a reference implementation), Informational, or Process. Each IEP moves through a status workflow of Draft → Proposed → Stable → Obsolete, with side paths for Deferred, Withdrawn, and Rejected proposals.

IEPs and the scope of ISO 24138

Several IEPs were contributed as input to ISO/TC 46/SC 9/WG 18, and the corresponding normative material was published in the standard. Others document ongoing community work that extends beyond the current edition.

  • Within the normative scope of ISO 24138:2024 - the ISCC structure, the standardized ISCC-UNITs (Meta-, Content-, Data-, and Instance-Code), the composite ISCC-CODE, and ISCC metadata.
  • Beyond the current standard - work such as the ISCC-ID, decentralized content registries, the ISCC DID method, and experimental Semantic-Codes. These may inform a future edition but are not part of ISO 24138:2024 today.

When precision matters, treat "contributed as input to ISO" and "published in the standard" as distinct claims, and consult the published standard for the definitive normative scope.

Open-source software

The specifications are made executable and verifiable through open-source software, released under permissive licenses:

  • iscc-core - the reference implementation of the standardized codec and fingerprinting algorithms. Its code is the reference software published as the normative electronic insert of ISO 24138:2024, and the foundation for all ISCC generation.
  • iscc-sdk - the high-level Python toolkit and primary integration entry point. It builds on iscc-core and adds content-type detection, metadata extraction and embedding, and content extraction so applications can produce a full ISCC-CODE directly from a media file.
import iscc_sdk as idk

# Generate a full ISCC-CODE from a media file
iscc_meta = idk.code_iscc("example.jpg")
print(iscc_meta.iscc)

Historical specification drafts

Before standardization, the ISCC was developed as a public working specification by Titusz Pan within the Content Blockchain Project. These early drafts predate ISO 24138:2024 and current implementations. They are superseded and retained for historical reference and URL continuity only:

For the history of how these drafts became an International Standard, see the History page.