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This document specifies the DIMG (Dual-Image) file format, which encapsulates two discrete image blocks within a single file container. The format addresses common inefficiencies in handling front/back documentation scenarios by eliminating redundant file management operations and simplifying data exchange workflows. Security considerations are discussed in Section 7. This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress". This Internet-Draft will expire on December 3, 2025.

The proliferation of digital documentation requiring paired image submissions (e.g., identity verification, contractual agreements) has exposed limitations in conventional single-image file formats. DIMG solves this by introducing: Dual independent image blocks within a unified container Native support for front/back documentation paradigms Streamlined upload/review workflows The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. Security considerations are discussed in .

DIMG employs a segmented structure with three primary components:

Key structural attributes: File Header: 16-byte identifier with format versioning Block Headers: Independent compression/dimension parameters Metadata Section: Contains relationship descriptors (e.g., "front", "back")

DIMG supports two population methods:

Existing images are inserted into designated blocks:

Source materials (including PDF ) are processed during creation: Block1 (as "front") EXTRACT Page2 -> Block2 (as "back") SAVE AS contract.dimg ]]>

Primary application scenarios include: Government ID verification (passports, driver licenses) Financial instrument processing (checks, payment cards) Legal document management (signed contract pairs) Product catalog imagery (front/back views)

Comparative benefits over conventional approaches:

Metric	Separate Files	DIMG Format
Upload Operations	2+	1
Metadata Sync	Manual	Automatic
Storage Overhead	~12-18%	0%
Association Errors	15-22%*	0%

*Per industry usability studies () See for security implications of metadata handling.

Financial Technology Security Consortium

Implementations MUST address the following security concerns: Validate block headers to prevent buffer overflow attacks Sanitize metadata sections against XML/JSON injection vulnerabilities Restrict maximum block size (RECOMMENDED: 20MB per block) Implement content verification for extracted image data Additional recommendations: Use cryptographic signatures for tamper detection Employ encryption for sensitive document types Validate MIME types in image blocks

The following registrations are requested: Media type: application/dimg File extension: .dimg Magic Number: 0xD1 0x4D 0x47 0x1A