Can a blurred screenshot be unblurred?

Usually not — if it was blurred hard enough. A solid box cannot be undone at all. A light blur, a coarse mosaic or a swirl sometimes can, and the thing that most often gives people away is not the blur but what they forgot to cover.

The short answer

• Solid box or fully opaque pen: cannot be reversed. The pixels underneath are gone from the file you share.
• Heavy blur (the text becomes a smooth smear with no letter shapes left): not practically reversible for ordinary text.
• Light blur or small-block pixelation over text: sometimes reversible, especially when the font is known and the text is short.
• Swirl, twirl and other distortions: reversible. They move pixels around rather than destroying them.

Why pixelation and light blur can leak

Screenshots are an unusually easy case for an attacker, because the text is set in a known system font, at a known size, on a clean background. If the set of possible values is small — a four-digit code, a date, a short amount — someone can render every candidate, blur or pixelate it the same way, and see which one matches. Tools for exactly this exist for pixelated screenshots; Depix, released in 2020, recovers text from mosaic-pixelated screenshots in a known font.

Distortion filters are worse. In 2007 police reconstructed the face of a suspect who had hidden it in his own photos with a swirl effect — the swirl only rearranged the pixels, so running it backwards brought the face back.

What a blur never hides

• Length and shape. A blurred email still shows roughly how long it is, and a blurred name still sits next to its avatar and the message it sent.
• Context. "Your code is ████" in a banking app tells a reader what kind of number it was.
• The second copy. The same phone number in the notification banner, the contact header and the message body — people cover one and post the other two.
• Your original. In Photos, Revert to Original undoes the edit on your own device. The copy you share is flattened; the one in your library is not redacted.

How to blur so it stays blurred

1. For a short, high-value secret, use a solid box. A one-time code, a PIN, the last four digits — the shorter it is, the more a solid cover beats any blur. iPhone's Markup does this for free; the steps are in how to blur something in a screenshot on iPhone.
2. If you blur, blur hard. You should not be able to tell there were letters there, let alone which ones.
3. Cover the whole string, including the first and last characters. Partly covered text is partly readable.
4. Never use the highlighter. It is translucent by design.
5. Read the screenshot like a stranger before you send it: banners, tab titles, avatars, the address bar, anything in the corner.

How Snapdraft blurs

Snapdraft looks for the things people miss — phone numbers, emails, addresses, card and account numbers, API keys, names, faces and QR codes — and blurs every one it finds, so you are checking its work rather than hunting. The blur is a Gaussian blur rendered into the pixels of the saved image, with a radius of at least 20 pixels that grows with the height of the line it covers, which leaves no letter shapes behind. It is not a layer and it cannot be moved aside.

It does not offer a solid box, so for a very short secret, Markup's filled shape is the better tool — and it is already on your phone. Snapdraft is free, runs on the iPhone and uploads nothing.