CleanorTools
Black Box

Black box image redactor

Details

How to use Black box image redactor

What the tool does, how to run it, and what to expect from the result.

How to put a black box over part of an image

A black box on a rasterised image is a real redaction: the pixels are overwritten and the export contains only the final result.

That is the property that makes it safe, and it is why an opaque box should be your default for anything readable.

  • Upload the image or screenshot.
  • Drag a rectangle over each piece of information that has to disappear.
  • Overshoot the edges so no partial characters remain visible.
  • Repeat for every region, checking corners, window titles and reflections.
  • Export as PNG, review at full zoom, and secure or delete the original file.

Why black boxes are still the clearest redaction

Sometimes the safest answer is also the simplest: cover the sensitive part completely. A black box communicates immediately that the content is intentionally hidden and should not be inferred.

That makes it useful for documents, screenshots, payment screens, admin interfaces, and any export where the masked area should be unquestionably unreadable.

Where this page helps most

This is best for people who already know they want black-box redaction and do not need the extra step of choosing between multiple masking styles.

  • Blacking out numbers and names in screenshots
  • Masking signatures and private details in documents
  • Redacting dashboard captures before publishing
  • Covering sensitive objects or faces in quick exports
Tips

Getting a better result out of Black box image redactor

Specific settings and thresholds, not general advice.

  • A black box is the only kind of image redaction that actually destroys information. The pixels in the rectangle are overwritten with #000000, and the file is re-encoded from that canvas, so nothing survives underneath.
  • This is the difference between redacting an image and redacting a PDF badly. A black rectangle drawn on a PDF page is an object sitting on top of text that is still selectable and copyable. Here the source is rasterised first, so the box is not an object, it is the pixel value.
  • Draw the box larger than the content. Partial characters, ascenders and descenders poking out at the edge of a box have been enough to reconstruct a name or a number more than once, and it costs nothing to overshoot by a few pixels.
  • Black boxes signal redaction. That is a feature in a document you are handing to a journalist or a court, and a drawback in a marketing screenshot, where a white box blends into a light UI. The white box tool exists for that case.
  • Export as PNG. JPEG compression puts ringing artefacts around the hard edge of the box, which looks sloppy on a document, and PNG is lossless so the box is exactly the colour you set.
Limits

What Black box image redactor does not do

The honest boundary, so you do not lose time finding it yourself.

  • It does not find sensitive content for you. Every box is a rectangle you draw.
  • The box is rectangular. An irregular region needs several overlapping boxes.
  • It does not redact text in a PDF, only in a rasterised image. A PDF needs a tool that removes the underlying text.
  • The original, unredacted file is still on your disk after export.
Reference

Terms used on this page

Short, plain-language definitions for the formats and settings above.

Editing & toolsImage redactionImage redaction permanently hides sensitive information in a photo or screenshot — names, account numbers, faces, addresses — by covering it and flattening the result so the hidden data cannot be recovered. Done correctly, the original pixels are destroyed, not just visually masked.GeneralPhotos & videoScreenshotA screenshot is an image captured of whatever is on your screen, saved into your photo library like a regular picture. Individually small, screenshots accumulate fast and clutter the camera roll because most are saved once and never needed again.iOSAndroidGeneral
At a glance

Who Black box image redactor is for

A quick way to understand who this helps, what it solves, and where it connects next.

Best fit

People redacting screenshots, documents, and photos where the hidden area should be fully unreadable

Ideal for

Strong image redaction with flat black boxes when blur or pixelation would still feel too soft

FAQ

Common questions

Short answers for the questions people usually have before trying a utility like this.

Why use a black box instead of blur?

A black box is stronger and more explicit. It fully covers the selected area instead of only softening it.

Can I change the box color on this page?

No. This variant is intentionally fixed to black-box redaction so the workflow stays focused on one job.

Does the image stay local?

Yes. The image is redacted and exported in the browser without server-side processing.

Is a black box a real redaction?

On a flattened image, yes. The pixels under the rectangle are replaced with black and a new file is encoded from the canvas, so there is no original data left in the exported image. That is what makes it different from blur or pixelation, which transform the pixels rather than destroying them.

Why is this safer than a black box in a PDF or a slide?

Because in a PDF or a slide the box is an object drawn above the content, and the content is still in the file. Anyone can move the box or copy the text underneath it. Here the image is rasterised and the box overwrites the pixel values.

How big should the box be?

Bigger than the content. Leave a margin so no part of a character, no ascender or descender, and no partial digit shows at the edge. Reconstructions have been made from less.

Can I use a colour other than black?

This page is locked to black. If you want white, or another colour, use the white box page or the general redact image page, which exposes the fill colour.

Does the file get uploaded?

No. The image is decoded, painted and encoded entirely in your browser.

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