Common metadata forgeries and how to spot them
Strip and relabel, transplant someone else's EXIF, change the dates, fake a Photoshop record. None of it is hard, and all of it leaves contradictions.
Why anyone forges metadata
To make an AI picture look like a camera shot; to make a stolen picture look like your own; to make a photo's time and place match a story; or the reverse, to remove an AI declaration and slip past platform checks.
Method 1: strip, then relabel
Remove all metadata, then write a single XMP block claiming CreatorTool is Photoshop. The signature of this method is XMP present, EXIF absent. A photo genuinely saved from Photoshop almost always keeps its EXIF, because that is Photoshop's default. AuditImage flags this as "Metadata contradicts itself".
Method 2: transplant EXIF
Copy the whole EXIF block from a real photo onto another picture:
exiftool -tagsFromFile real.jpg -all:all fake.jpg
The EXIF is perfectly self-consistent because it is real. The cracks are elsewhere: resolution that does not match the camera model, an EXIF thumbnail that differs from the main image, JPEG quantisation tables that are not that camera's style, no MakerNote in that vendor's layout. AuditImage does not compare quantisation tables yet, but it shows the thumbnail and resolution for a manual check.
Method 3: change the dates
Set DateTimeOriginal to the desired time but forget the XMP CreateDate, photoshop:DateCreated, or the stEvt:when entries in History. AuditImage compares the EXIF capture time with the XMP create time and flags a difference of more than a minute.
Method 4: a fake derivation
Write xmpMM:DerivedFrom so the picture appears to be "edited from some original", without writing xmpMM:History. A real editing workflow produces both together. AuditImage flags "claims derivation but has no edit history".
Method 5: remove the AI declaration
Delete the C2PA manifest, DigitalSourceType, the PNG parameter block. This leaves no contradiction, only a blank. AuditImage's verdict becomes "No usable metadata" and nothing more can be said. This is why metadata can only ever incriminate, never exonerate.
Method 6: forge C2PA
In principle you can sign a manifest yourself. The crack is the signer certificate: a self-signed or test certificate has a subject like FOR TESTING_ONLY and is not on the CAI trust list. AuditImage shows the certificate subject and issuer for you to judge; for strict verification use CAI Verify or c2patool.
The general principle
In a real file the metadata segments were written naturally by different programs at different times, and they agree with each other. A forger usually edits only the fields they thought of. So look at consistency, not at any single field. AuditImage's findings section is built on exactly that idea.