How to blur personal information in a screenshot

Screenshots are how most work gets explained. A bug report needs one, so does a support ticket, a question in a team chat, a how-to document, a slide. And most of the pages worth capturing have someone’s details on them: a customer record, an inbox, an order, an account settings page.

The usual routine is to take the screenshot first and clean it up afterwards: open it in an editor, draw a box or a blur over the parts that shouldn’t be there, save, send. It works most of the time. When it doesn’t, the image has usually already been sent.

Why editing afterwards goes wrong

The first problem is missing something. You cover the email address you were worried about, and miss the same address in the page header, the customer’s name in a breadcrumb, a phone number in a notification that happened to be on screen, or a browser tab whose title names another client. Small text is easy to miss at the size you’re editing it, and the more screenshots you take, the more likely one of them gets through.

The second is that some edits hide less than they appear to. In 2022 a researcher at the security firm Bishop Fox released a tool called Unredacter and used it to recover text that had been hidden by pixelation. His advice afterwards was blunt: to hide text, cover it completely with black bars, and don’t rely on pixelation or blurring. Light blurs and small pixel blocks keep enough of the original shape for software to work out what was underneath.

Cropping isn’t always deleting, either. In 2023 two researchers found that the Markup tool on Google Pixel phones, and later the Windows Snipping Tool, could leave the cropped-out part of an image inside the saved file when you saved over the original. The bug, nicknamed aCropalypse, meant parts of “cropped” screenshots could be recovered. Both have since been fixed, but images saved before the fixes still carry the extra data.

And editing takes time, which is why it gets skipped. A quick screenshot for a colleague rarely gets the same care as one for a customer.

Blur the page first, then take the screenshot

The more reliable order is the opposite: hide the details on the page itself, check what’s on screen, and only then capture it. Whatever screenshot tool you use then captures a page that never showed the details in the first place. There’s nothing to forget to edit, and nothing hidden in the file.

It also scales. If the same kinds of details appear on every page you capture, such as emails, phone numbers and customer names, you can have them hidden automatically instead of covering them one screenshot at a time.

How to do it with Smart Blur

Smart Blur is a browser extension that blurs personal information on web pages, on your computer. Nothing is uploaded and there’s no account. Everything you need to blur a page before a screenshot is free:

• Patterns blur email addresses, phone numbers, card numbers, US Social Security numbers, IBANs, IP addresses and API keys automatically as the page loads. You can add your own patterns for things like order numbers or bank account numbers.
• Keywords to hide blurs specific names wherever they appear on the page.
• Click, Draw and Text cover anything else: click an element, drag a box over an area, or select a piece of text.
• Tab names hides the titles and icons in your browser’s tab bar, in case it’s in the picture.

Once the page looks right, take the screenshot the way you normally would: Cmd+Shift+4 on a Mac, Windows+Shift+S on Windows, or any other tool. Because the blur is part of the page, the screenshot includes it.

Smart Blur Pro adds a Screenshot button to the panel. It captures the visible area or a region you select, with the blur already in it, and copies the image to your clipboard ready to paste. Smart Blur’s own panel and buttons are never in the shot. Alt+Shift+S repeats your last capture.

Make the blur strong enough

A blur on screen and a blur in a file someone can zoom into aren’t the same thing. Smart Blur’s blur strength is set under Settings → General → Blur Intensity, on a scale of 0 to 10. For screenshots that will travel, such as attachments to tickets, images in shared documents or anything public, turn it up to the maximum. A stronger blur leaves far less of the original text’s shape behind.

Even a strong blur shows roughly how long the hidden text was. For most screenshots that doesn’t matter. When it does, or when the redaction has to stand up to scrutiny, as in legal documents, records requests or anything published, use solid boxes. If the document is a PDF, PDF Redactor removes the text under its black boxes rather than covering it.

A few habits that help

Check the screenshot, not the page. Open the image before you send it and look at it at full size, the way the person receiving it will.

Capture less. A region or a single window is easier to check than your whole screen, and contains less to miss.

If you use Smart Blur Pro’s Local AI to find names and addresses, give it a moment after a page loads: it scans the page in the background, and the panel says “Scanned this page” when it’s done.

Smart Blur works on web pages in Chrome, Edge and other Chromium browsers. For desktop apps, you’ll still need to edit the screenshot, so cover the details with solid boxes and save the result as a new file rather than over the original.

For the same approach on live calls, see 10 screen sharing best practices for safer meetings.