Scanned document metadata: what printers and scanners embed
A scanned page looks like a plain picture of paper. It usually isn't just that. Scanners and printers can leave two very different kinds of trace behind: ordinary file metadata that any device would add, and — on some color laser printers — tracking dots printed right onto the page itself, invisible to the naked eye.
The metadata part
When you scan a document to PDF or image, the scanner or the software driving it typically writes metadata into the file: the device's make and model, sometimes a serial number, the software version, and a timestamp of when the scan happened. If the scan went through a phone camera app instead of a dedicated scanner, you get the same EXIF fields a regular photo carries — including GPS, if location services were on.
None of this is visible when you open the file and look at the page. It's sitting in the file's header, the same way a photo's EXIF block sits behind the picture. Anyone who receives the file and knows where to look can read it.
The tracking-dot part
This is the one that surprises people. Many color laser printers, by design, print a faint grid of yellow dots on every page — a pattern too small and low-contrast for most people to notice, but readable under blue light or magnification. It's typically used to encode the printer's serial number and a timestamp, a feature manufacturers added years ago at the request of anti-counterfeiting regulators. It's a property of the printed page itself, not a file — scrub doesn't touch printed paper, and there's no software fix for a dot pattern already on a physical sheet. If it matters to you, the honest options are checking your printer model's documentation or using a printer known not to add the pattern.
What scrub actually covers here
scrub works on the file, not the paper. For a scanned image (JPEG/PNG) it removes EXIF, XMP and appended data the same way it does for any photo — losslessly, on your device. For a scanned PDF, scrub currently detects hidden content — metadata fields, embedded text layers, author/producer info — and shows you what's there; PDF cleaning isn't available yet, so treat a scan-to-PDF workflow as scan-and-check for now, not scan-and-clean.
If you need a scanned document actually stripped of metadata today, export it as an image first, clean the image with scrub, then rebuild the PDF — or wait on PDF write support and don't assume it's handled in the meantime.
The short version
Scanned files can carry a device serial number and timestamp in their metadata — checkable and, for images, removable today. Printed tracking dots are a different, physical thing scrub can't touch. Know which one you're dealing with before you send a scan out. Get scrub free and see what's actually in a scanned file.