Can you stop someone screenshotting a document?

Some products in this category say yes. Some, to their credit, say no. The truthful answer is more useful than either, and it changes what you should buy.

Why a website cannot block screenshots

When you press Cmd+Shift+4 on a Mac, or Power+Volume Down on a phone, the operating system captures the screen buffer. The browser is not consulted. The web page is not notified. There is no JavaScript event for "a screenshot was taken", because the screenshot happens at a layer far below the page.

This is not an oversight that a clever developer can work around. It is a deliberate boundary in how operating systems are built, and it applies equally to every website, including every "screenshot-proof" document sharing service you have been pitched.

What a web page can do is genuinely useful, but it is deterrence rather than prevention:

• Blur the content the instant the window loses focus, which defeats casual capture tools that require you to click away first.
• Block the print, save and copy keyboard shortcuts, and disable right-click.
• Never deliver the original file at all, so there is nothing to download and forward.
• Watermark every page with the viewer's identity, so any capture that does happen names the person who took it.
• Reveal only a small area at a time, so a capture contains very little.

What each platform actually allows

This is the table most vendors will not show you.

Platform	True screenshot blocking?	Reality
Android app	Yes	FLAG_SECURE makes the window come out black in screenshots and recordings. Enforced by the OS.
iPhone / iPad app	No	Apple provides no equivalent for normal app content. An app can detect a screenshot after it happened, and can detect active recording and hide content. DRM video is the exception.
Windows app	Partly	SetWindowDisplayAffinity excludes a window from common capture APIs. Microsoft is explicit that it is not a complete guarantee.
macOS app	Partly	Apple warns its window-sharing controls should not be relied on to hide content from capture.
Any web browser	No	The page is never told. Deterrence and detection only.
Second phone photo	No	Impossible to prevent, on every platform, forever.

The camera problem nobody solves

Every conversation about screenshot prevention eventually hits the same wall: a person can point another phone at the screen. No amount of software prevents this. If a vendor's marketing implies they have solved it, they are either confused about their own product or being dishonest with you.

The only meaningful defence is to reduce how much is legible at any one moment. If the document is blurred except for a small area under the reader's finger, a photograph captures one sharp patch and a page of grey. If a password reveals one line at a time, a photograph can never catch the whole credential set. This does not make capture impossible. It makes the capture worth very little, which is the point.

What actually prevents leaks

Here is the uncomfortable thing about this market: prevention is largely theatre, and attribution is what works. People do not leak documents that visibly carry their own name and mobile number. The deterrent is social and legal, not technical.

So the properties that matter are:

• Identity binding. The viewer states who they are, and ideally verifies it, before anything is shown.
• Identity watermarking. Their name and number across every page, ideally burned into the rendered image rather than sitting in an overlay that can be stripped.
• Value reduction. Reveal a small area at a time. Show secrets one line at a time.
• An audit trail. Who opened it, when, from where, for how long, and what they attempted.
• Revocation. The ability to withdraw access after sending, including mid-view.
• No file delivered. If the recipient never receives a file, there is nothing to forward.

How to tell an honest vendor from a dishonest one

Ask one question: "Can someone photograph the screen with another phone?"

If the answer is anything other than an immediate yes, walk away. It is the single fastest integrity test in this category, and it costs you nothing. A vendor who will misrepresent a physical impossibility will misrepresent their encryption too.

Then ask which platforms support real screenshot blocking. The correct answer is: Android yes, iOS no, browsers no, Windows partly, macOS partly. If you get "all of them", you now know exactly what you are dealing with.

Honest vendors describe their protection as capture-resistant, not screenshot-proof. The vocabulary tells you a lot.

Credit where it is due: not everyone in this market overclaims. Locklizard states plainly that you cannot stop webpage screenshotting and that a camera pointed at a screen defeats any software. Microsoft describes its own protection as "a visual deterrent", and Microsoft owns the Windows capture APIs. Those are the honest end of the market. The dishonest end claims a browser can block OS-level screenshot commands, which is not a thing a browser can do.

Where SightSealer stands

Since this is our page, the same standard should apply to us.

SightSealer's browser tier cannot stop screenshots and we do not claim it does. What it does: encrypts your content in your browser so we cannot read it, watermarks every page with the viewer's name and number, reveals only a small area under the cursor, shows secrets one line at a time, blurs on focus loss, blocks print and copy, delivers no file, logs every view, and lets you revoke access mid-view. True OS-level screenshot blocking arrives with the native app tier on Android, and on iOS it will do what iOS permits, which is detection rather than prevention.

That is less than our competitors promise. It is also true.