Privacy
A device identifier hiding in MakerNotes
Some cameras and phones write a body or sensor serial into metadata, which links every photo from that device to each other.
Guides on Privacy: Who could see it, how, and what each path costs to close, Soft delete, backups, caches and logs, Sometimes, and the policy clause that says so is easy to miss
Yes, some cameras and phones write their own serial number, or a sensor identifier that works like one, into every photo's metadata. No viewing app shows it, and it needs no GPS field or account to do its job: any two photos carrying the same number came from the same physical device.
Why it exists
Manufacturers use these fields for their own purposes - warranty tracking, forensic verification for professional and press photography, internal diagnostics. None of those purposes require your knowledge or consent at the point the photo is taken, so the field is written automatically as part of normal capture, the same way exposure settings are. Coverage is inconsistent: some camera bodies and phone models write a serial or sensor ID, others do not, and manufacturers rarely document which fields they populate.
Why it matters more than it looks like it should
A serial number carries no meaning by itself - it is not a name or a location. What it does is link. Two photos, uploaded months apart to different places, with no shared filename, no shared account and no shared visible content, can still be tied to the same device if both carry the same serial. That linkage is exactly the kind of fact that turns several separately-shared, individually anonymous-seeming photos into a set - which is a stronger privacy exposure than any single photo on its own, in the same way several weak identifiers converging is worse than one strong one.
Where the field lives and why it is easy to miss
The Exif standard has a field for it: ExifTool's tag reference lists tag 0xa431, "called BodySerialNumber by the EXIF spec," alongside a LensSerialNumber tag. Where a maker uses its own field instead, the identifier typically sits in the MakerNotes block (tag 0x927c), a manufacturer-specific area of the file that generic "remove metadata" tools do not always parse, because it is undocumented and varies by brand. A tool that clears the standard EXIF fields, including GPS, can leave MakerNotes intact if it was not built to handle them specifically. The routine covered in stripping EXIF before you upload removes the common fields reliably; whether it also reaches MakerNotes depends on the exact method used, and checking with a tool that lists every block - not just the standard ones - is the only way to be sure.
What to do about it
Stripping metadata fully, rather than only the location field, is the direct fix, and it needs doing once per photo rather than once per device. A screenshot of the image, rather than the original file, avoids the problem structurally, since a screenshot carries a fresh set of fields describing the screenshot itself rather than the camera that took the original.
None of this affects how a rating model scores the pixels or how a fixed measurement method works; it is purely about what travels with a file after it leaves your device, whether to a rating tool, a human reviewer, or anywhere else. Rate Cock is one option among several worth checking on exactly this point, and comparing how services actually handle metadata rather than assuming is the only reliable way to know.