JPEG structure

List a JPEG's marker segments and quantization tables, or produce an Error Level Analysis image to spot re-compression artifacts.

JPEG structure lists a JPEG's marker segments by name, length and offset, decoding SOF dimensions and every DQT table's min, max and average. With ela on, it makes an Error Level Analysis image instead, the re-encoded difference amplified tenfold at quality, default 75. A file missing the SOI marker is refused. A bright ELA region only marks a bigger re-compression gap.

Questions

What are the two modes?

The default segment table, listing every marker, its length and offset, or, with ela on, an Error Level Analysis image instead.

What does the DQT table row show?

For each quantization table: its table ID, bit precision, and the minimum, maximum and average of its 64 values.

How does Error Level Analysis work?

It re-encodes the image at quality, default 75, and shows the pixel difference from the original, amplified 10 times.

What does a bright region in the ELA image mean?

That area differs more from its own re-compression than the rest of the image, a possible sign of localized editing, not proof of it.

What happens with a truncated or malformed file?

It reports how far it got and notes issues like a missing EOI marker rather than stopping silently.

What if the file has no SOI marker?

The tool refuses it as not a JPEG file outright.

Compare

Tool	Runs on the CLI	Live as you type
JPEG structure	Yes	No
Parse ASN.1	Yes	No
Parse Object Identifier	Yes	No
TLV / Tag-Length-Value parser	Yes	No
ELF info	Yes	No
PNG chunks	Yes	No
ZIP structure	Yes	No

Related Forensics tools

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