Image magic numbers and container signatures

Starts with the JPEG start-of-image marker followed by a marker byte.

Reads a bounded start-of-frame segment; no pixel data is decoded.

JPEG is reported as a still image. Embedded thumbnails are not counted as images.

Uses the complete eight-byte PNG signature and validates bounded chunk lengths.

Reads width and height from a valid IHDR chunk.

An acTL chunk before IDAT identifies APNG animation and declares its frame count.

Requires an exact GIF87a or GIF89a logical-screen header.

Reads the little-endian logical-screen width and height.

Walks bounded extension and image sub-blocks; two image descriptors prove animation.

Requires both the RIFF marker and WEBP form type, then validates bounded chunk sizes.

Reads VP8, VP8L, or VP8X dimension fields without decoding pixels.

Uses the VP8X animation flag and ANIM/ANMF chunks when present.

Validates the ftyp box and distinguishes its major and compatible brands.

Uses a structurally valid, bounded ispe property when one is available.

msf1 and sequence brands prove a sequence; other HEIF containers remain unknown.

Validates the ftyp box and requires the avif or avis major/compatible brand.

Uses a structurally valid, bounded ispe property when one is available.

The avis brand identifies an AVIF image sequence.

Requires a valid little-endian or big-endian TIFF header and bounded first-IFD offset.

Reads ImageWidth and ImageLength from bounded IFD entries.

A non-zero next-IFD pointer proves another page; otherwise the state is conservative.

Requires the BM signature and a supported bounded DIB header.

Reads dimensions from BITMAPCOREHEADER or BITMAPINFOHEADER-compatible fields.

BMP is a single still-image container.

Validates the reserved field, icon type, count, and bounded directory table.

Reads dimensions from resource directory entries; zero represents 256 pixels.

Multiple directory entries are reported as multiple embedded icon images.

Validates the reserved field, cursor type, count, and bounded directory table.

Reads dimensions from resource directory entries; zero represents 256 pixels.

Multiple directory entries are reported as multiple embedded cursor images.

Scans only a bounded UTF-8 preamble and accepts XML declarations, comments, and doctype text.

Reads simple numeric width/height attributes or a four-number viewBox when present.

Bounded animate/set elements can prove animation; absence may remain unknown.

Finds a PDF header within the permitted leading-byte window and checks the bounded tail for %%EOF.

Page dimensions are not inferred by the signature inspector.

Page and embedded-image counts require a PDF parser and remain unknown here.