Watermarking Copies of Your Passport and IDs

How to mark a document copy so it cannot be reused

A passport scan ends up in other people's hands more often than you might think. A landlord wants it for the tenancy agreement, a letting agency to hold a property, an employer before you start, a courier service for an authorisation letter. The deal ends, but the file stays behind in someone's inbox, in a manager's messaging app, in a shared office folder.

You cannot recall a copy. What you can do is make sure in advance that it is fit for exactly one purpose and looks suspicious in any other. To do that, you put a line of text on the copy: who it is for, why and when.

What a line of text on a copy achieves

A clean passport scan is universal. It can confirm your identity anywhere the document is checked from a picture rather than against the original. That universality is precisely what makes a leak dangerous.

A line reading "Copy for Northgate Lettings, tenancy agreement, 10 Oct 2026" takes that universality away. Anyone shown such a copy in another context sees at once that the document was not meant for them. If you burn the mark into the image (more on that below), the line can only be replaced by redrawing the page, and that shows.

It helps to understand the limits. The text does not legally forbid anyone from using the copy, and it does not encrypt the data. It works as a label: it makes reuse visible and lowers the value of the file to someone who wants to pass it off as a fresh copy.

What exactly to write

A good line answers three questions.

Who: the name of the organisation or the recipient's surname. Without it, a copy leaked from one company works just as well for any other.

Why: "tenancy agreement", "booking", "building pass". The purpose rules out scenarios such as taking out a loan or signing up for some unrelated service.

When: the date you handed it over. An old date on a copy raises questions with anyone expecting a recent document.

Shorten a long phrase. The text repeats across the page many times, and the shorter it is, the more densely it covers the details. "For Northgate Lettings, tenancy, 10 Oct 2026" reads just as well as the full version.

How to add a text watermark

1. Open add-watermark and upload the PDF with the copy. 2. Type your line into the text field. Do not leave the field empty: in that case the service name lands on the page instead of your label. 3. Choose the opacity and font size. 4. Start processing and open the result in full, going through it page by page.

By default the text is laid across the whole page in a grid at a 45-degree angle. That is the right mode for document copies: a single line in a corner is easy to crop off or paint over, whereas a diagonal grid running across every field cannot be removed that way.

If you need one neat line, for example in an empty margin area where it will not cover any text, you can place it as a single stamp: drag the box on the page preview to where you want it, and the mark lands at that spot as one stamp on every page.

Opacity and size: legibility versus protection

The text is grey, and opacity can be set from 5 to 95 percent, with 35 as the default. Font size goes from 10 to 120, defaulting to 42.

For a passport copy, the useful opacity range is 30 to 45 percent. Below that the text gets lost against the grey background of the form and is hard to see on a printout. Above it, the text starts covering the document number and date of birth so heavily that the recipient cannot read them and asks you to send the copy again, this time unmarked.

With size, the logic is this: the line should cross the fields containing data rather than fit between them. At 30 to 50 points on an A4 page, each row of the grid passes through the photo and the text fields at the same time. A very large font produces a sparse grid that leaves clean patches between the rows.

Check the result on a phone. That is where the recipient most often looks at the copy, and a line that looks light on a monitor can swallow the digits on a small screen.

Why an ordinary watermark can be removed

The mark is placed on the page as a separate layer, and the content underneath remains untouched. There is an upside: a text document keeps its text layer after processing, so search and copying still work and the file size barely grows.

The downside is that a separate layer can also be deleted separately. Someone with a PDF editor selects the objects that make up the text, erases them and is left with a clean page. For an internal draft marked "Draft" that hardly matters. For a passport copy going to a stranger, it does.

The fix is straightforward: after adding the watermark, redraw the pages as images. The text then stops being a separate object and becomes pixels in the same picture as the data.

How to burn the mark into the image

The easiest way is to run the finished file through pdf-to-grayscale. The tool renders each page as a grayscale image and builds a new PDF from them. The mark and the data end up in one raster, and the text can no longer be selected on its own.

This step has three consequences you should accept knowingly.

Colour is lost. For a passport copy this is no problem and arguably a benefit, since such copies are usually made in black and white anyway.

The text layer goes too. A scan never had one in the first place, but a typed contract will no longer be searchable or copyable after this step.

The size may change. A colour scan usually gets lighter, while a text document becomes noticeably heavier, because every page turns into a picture.

If you need to keep the colour, the same result comes from a two-step chain, PDF to JPG and then JPG to PDF: the pages become pictures and are assembled back into a document.

An image watermark instead of text

For documents sent on behalf of a company, people sometimes use a logo or a stamp instead of a line of text. That is what add-watermark-image is for: it adds a picture to the PDF, ideally a PNG with a transparent background.

The picture is placed once per page, either in the centre or in one of the four corners. Its width is set as a share of the page width, from 5 to 100 percent, with 28 as the default. Opacity is adjusted the same way, from 5 to 95 percent.

For protecting copies, an image mark is weaker than a text grid. A single logo in a corner covers a small part of the page and is easier to cover up. It works well as the sender's signature, not as a label of purpose. If you want both, add the logo first and then a text grid with the purpose and date on top of it.

The order of steps for a copy going out

The sequence matters, because each step builds on the one before.

1. Remove anything unnecessary. If the recipient only needs the photo page, do not send the page with your address. Black out fields they do not need in redact-pdf: there the content under the area is genuinely deleted, not hidden beneath a rectangle. 2. Add a watermark with the purpose and date. 3. Burn it into the image by converting to grayscale. 4. Check the result: open the file and try to select the text with your mouse. If it does not select separately from the page, the mark has become part of the picture.

Adding a password with protect-pdf makes sense if the file travels by email or through cloud storage where outsiders might see it. Bear in mind, though, that restrictions such as "print only" are not respected by every viewer. It is the open password that encrypts the file, while copy restrictions are only advisory.

When you do not need a watermark

Not every copy is worth marking.

Government portals and official systems verify the document themselves and expect a clean scan. Text over the details can get your submission rejected, and a watermark would not prevent a leak through a government system anyway.

Banks and solicitors who compare the copy against the original in front of you usually make their own copy. There is no reason to hand over your marked one there.

Documents that will be signed and returned are better marked with a single line in the margin rather than a grid: a grid gets in the way of signatures and stamps.

If in doubt, ask the recipient beforehand whether they will accept a marked copy. Private landlords, employers and agencies usually don't object.

What a watermark does not do

It does not hide data. Everything visible on the copy stays visible under the text. If the recipient does not need a particular field, it should be removed, not labelled.

It does not stop anyone from photographing the screen or a printout. All it does is make it obvious what the copy was issued for.

And it is no substitute for common sense: the safest copy is the one you never sent. Before forwarding a passport scan, it is worth asking whether the recipient needs the whole thing or whether a contract number and your full name would do.