How to blur part of an image online (free, no upload, no watermark)

Quick answer: 712tools' Blur Brush is a free, in-browser tool that lets you paint blur or pixelation over any part of an image - a face, a license plate, a credit card number, an address, a chat handle in a screenshot. Nothing uploads. Nothing is stored. You download a PNG at original resolution with no watermark, no account, no cap. Skip to the tool if that's what you needed; the rest of this post is the safety details most search results don't cover.

The two reasons people search for "blur part of an image"

Almost every "how do I blur part of a photo" query comes from one of two situations:

1. Sharing a screenshot online - a Slack conversation, a WhatsApp thread, a payment confirmation, a customer support DM - and one part contains a name, phone number, address or ID you don't want on Twitter.
2. Posting a photo - of a friend, a stranger, a car, a house, a school pickup - where one face or identifier shouldn't be visible.

The tools that dominate Google for this - Fotor, Canva's blur, Pixlr's blur, TinyImage - all do the same thing under the hood: upload your image to a server, apply a filter, hand you back a download. That's a strange workflow for exactly the use case where you're trying to hide sensitive information - the image goes through a third-party server because it contains something you want redacted.

That's the whole reason 712tools' Blur Brush exists. It runs 100% in your browser via the Canvas API. Your photo never leaves your device. There is no server it could leak from.

How to blur part of an image, step by step

Open /image-blur-brush. Then:

1. Drop or upload the image. PNG, JPG, WEBP all work. Large screenshots (2000×3000) are fine.
2. Set the brush size. For a face in a group photo, start around 60px. For a car license plate at street distance, 30-40px. For a phone number in a screenshot, 50-70px depending on font size.
3. Set the blur strength. For faces and plates, 15-25px of Gaussian blur is enough to be unreadable. For credit card numbers, go higher - 30-50px, or switch to pixelate mode.
4. Choose the mode. Gaussian blur looks natural. Pixelate looks intentional. Use pixelate for anything that must be obviously redacted (legal screenshots, evidence, court exhibits).
5. Paint. Click and drag over the part you want to hide. Multiple strokes stack. You can undo any stroke, redo it, or clear the whole mask and start over.
6. Download the PNG. Full resolution, no watermark, no signup.

That's the whole tool. There's no learning curve - it's paint over what you want gone.

The mistake that makes blur reversible

This is the part almost every "blur online" tutorial skips, and it matters:

A small blur radius applied to a small feature is not always safe. Researchers have published multiple attacks - most famously in 2016, and again with more sophisticated attacks through the 2020s - showing that low-radius Gaussian blur applied to small text (credit card numbers, license plates, small serial numbers) can sometimes be reversed via deblurring neural networks, especially when the original font, background and lighting are known.

The rules that make blur genuinely safe:

• For text (credit card numbers, phone numbers, addresses, names in screenshots): use pixelate at a block size of at least 10-15px, or use Gaussian blur with a radius larger than the character height. If the digits are 20px tall, the blur radius should be 30-40px.
• For faces in low-resolution photos: low blur is fine - there's not enough signal to recover.
• For faces in high-resolution photos (4K+): use a larger blur radius or pixelate. Low-radius blur on high-res faces has been shown to be partially reversible.
• For anything that must be legally unrecoverable - court exhibits, medical records, redacted government documents - use pixelate with a block size at least twice the character height. Or better: place a solid black rectangle. In the Blur Brush, that's "pixelate at maximum block size" combined with a very high strength.

Pixelate is generally safer than blur for text. Blur retains some frequency-domain information that neural networks can sometimes exploit; pixelate throws it away irreversibly (a block of 400 pixels averaged to one value is one value - the other 399 are gone).

The five things people most commonly blur online

Based on search volume and support-request patterns in image tools, here's what people are actually redacting:

1. Faces in group photos. For social media privacy - friend's kids you don't have permission to post, strangers in the background of a vacation photo. Gaussian blur at radius 15-25 is fine at typical Instagram resolutions.

2. License plates. Selling a car online (Craigslist, Facebook Marketplace, Carvana), posting your rental car in a road-trip photo, sharing a parking-ticket screenshot. Use pixelate at block size 12-15, or heavy blur (30px+). The characters are small and legally identifying.

3. Credit card numbers. Sharing a payment confirmation, a receipt, a "look at this weird charge" screenshot. Always pixelate, never blur. Or place a solid rectangle. The security stakes are high enough that "probably safe" isn't good enough.

4. Addresses. Package delivery screenshots, real estate photos where a house number is visible, Google Maps screenshots showing a home. Pixelate the number and street name; a solid rectangle over the whole line is even safer.

5. Chat handles and screen names. Screenshots of Discord, Slack, WhatsApp, Instagram DMs. Blur the display names and profile pictures. If the conversation itself is sensitive, blur the message content too - or crop the screenshot before sharing.

Why in-browser matters for this specific task

I keep circling back to this because it's the whole point. Redaction is the one image-editing task where uploading to a server is philosophically weird:

• You're editing the image because it contains something you don't want shared.
• The tool you're editing with is a third party you have no relationship with.
• Their privacy policy might say "we don't store your images." It might. Some do. Most say "we may retain images for X days to improve service."
• Even if the policy is honest, servers get breached. TSA face-scan images, US Customs travel photos, GoDaddy customer data - all have leaked in the last five years, not through malice but through routine security failures.

An in-browser blur tool has none of those risks because there is nothing to breach. Your image is in your browser tab. When you close the tab, it's gone. Your redacted PNG is a download on your machine. No copy exists anywhere else.

If your redaction is casual (blur the friend's kid before posting a vacation pic), the risk of an upload-based tool is low. If your redaction is important (financial, medical, legal, an ongoing personal safety concern), an in-browser tool is the only reasonable choice. 712tools' Blur Brush is that.

Common questions

Does it work on PDFs? Not in v1 - the tool handles PNG, JPG and WEBP. If your source is a PDF, take a screenshot of the page first (macOS: ⌘⇧4; Windows: Win+Shift+S), then blur the screenshot, then re-embed if you need a PDF back. We may add native PDF support later.

Does it support video? No - video blur is a separate problem (frame-by-frame consistency, temporal filtering). For now use a screenshot of a single frame, or export the specific frame you want to redact.

Can I use the exported PNG commercially? Yes. Whatever rights you had to the original image, you still have. The tool adds no restrictions.

How big can the image be? Bounded by your device's memory. On modern laptops, images up to ~6000×6000 pixels are smooth. On phones, ~3000×3000 is comfortable.

What if I need to blur the same spot on many photos? For now the tool is per-image. If this is a common workflow (e.g. batch-blurring faces in a photo shoot), let us know - batch blur with saved brush strokes is a plausible v2 feature.

Related tools for the same workflow

• Background Remover - when the entire background needs to go (transparency), not just parts.
• Image Compressor - the redacted PNG is often large; shrink it before uploading to a chat/email.
• Image Resizer - resize to the exact dimensions for a platform (Instagram, LinkedIn, Twitter card).
• Image Converter - convert between PNG, JPG, WEBP after redaction, if the destination platform needs a specific format.
• Screen Recorder - if you're screen-recording something with sensitive info, capture it, then blur individual frames after.

Redaction is one of the few image-editing tasks where "which tool" genuinely matters, because "the tool that uploads your unblurred original" is the wrong answer even when the output PNG looks identical. Do it locally: Blur Brush.