You've done it hundreds of times without thinking about it.
Your photo is too large to email. Your website is loading slowly because the images are too big. Your client needs the file under a certain size. So you open a browser tab, type "free image compressor," drag your photo in, and get a smaller version back in seconds.
Simple. Free. Done.
Except there's one part of that transaction you probably never noticed.
Your photo left your computer.
What Actually Happens When You "Compress" a Photo Online
When you drag an image into TinyPNG, Compress.io, or most other free online tools, here's the real sequence of events:
Your photo travels across the internet to a server somewhere. That server, owned by a company you've probably never heard of, running software you can't inspect, processes your image. Then it sends the smaller version back to you.
The whole thing takes two or three seconds. It feels instant. It feels local. It feels like the tool is just doing something clever on your screen.
It isn't. Your photo made a round trip to a datacenter and back.
For a photo of your lunch, that's probably fine.
But think for a moment about what you've compressed over the years.
The Photos You Forgot You Uploaded
Client work you were under NDA not to share. Passport scans. Photos of your home, your car, your children. Screenshots that happened to contain your email, your account number, your address. Medical images. Legal documents you photographed on your phone. Confidential presentations. Unreleased product designs.
Every one of those went to someone else's server before it came back to you.
Most of the time, nothing bad happens. These companies aren't villains. But three things are true simultaneously:
You didn't know it was happening. The tools don't say "your file will now travel to our servers." They just do it.
You agreed to it. Buried in the terms of service, the ones nobody reads, is language describing exactly this. You consented without knowing you consented.
You had no alternative. Until recently, there genuinely wasn't another way. Compressing an image required a server to do the heavy lifting. Your browser wasn't capable.
That last part changed. Quietly, without announcement, browsers became powerful enough to handle image compression entirely on their own.
The Tool That Stays Silent
I built zeropng.com because I needed a compressor I could use on client files without worrying.
The experience looks identical to TinyPNG. You drag photos in. You get smaller photos back. There's a quality slider, format options, a download button.
The difference is invisible unless you know where to look.
Open the browser's developer tools. Go to the Network tab, the section that shows everything your browser sends and receives over the internet. Compress a photo on zeropng.com. Watch the Network tab.
Nothing moves.
No upload. No server request. No data leaving your machine. The compression happens entirely inside your browser tab, using technology that's been quietly built into every modern browser for years. Your photo goes in, a smaller photo comes out, and the whole process happens in the same place you're sitting.
You can test this yourself in thirty seconds. That silence is the entire point.
Who Actually Needs This
Freelancers and designers who work under NDAs. When a client says "don't share our unreleased work," they mean it, including with the servers behind your compression tool.
Small business owners who photograph products, receipts, documents. These files contain more sensitive information than most people realize.
Anyone in healthcare. Patient photos, scan images, medical documentation, these have legal protections that most free online tools don't comply with. A tool that never receives your files can't violate those protections.
Parents who share photos of their children. Location data is embedded in smartphone photos by default. Most people don't know this. That data survives compression unless the tool explicitly removes it, which zeropng.com does automatically, because re-encoding through the browser strips the original metadata.
Anyone who's ever thought "I probably shouldn't run this through an online tool", and then done it anyway because there was no other option.
Now there is.
The Question Worth Asking About Every "Free" Tool
Nothing is actually free. When a tool costs you nothing, the question worth asking is: what is the business model?
For image compressors, the answer has historically been: volume, data, and advertising. They need your files to pass through their servers to show you ads around the experience, gather analytics, and in some cases use uploaded content to improve their own AI models again, usually disclosed somewhere in the terms, and almost never noticed.
A tool that never receives your files has none of those revenue streams. Which means it has to find a different model or, in the case of zeropng.com, simply be free because it costs almost nothing to run. There's no server to maintain. No storage. No bandwidth bill for processing millions of images. Hosting a single HTML file on Cloudflare costs essentially zero.
The privacy isn't an added feature. It's a consequence of the architecture. The tool can't collect your data because it never touches your data.
It Also Works Without the Internet
This is the part that surprises people most.
After the page loads, zeropng.com works completely offline. You can open it, disconnect your WiFi, and compress photos. Everything runs inside the browser tab. There's nothing to connect to.
This makes it useful in places and situations where you might not have assumed a web tool would work, on a plane, in a location with unreliable connection, on a device with restricted network access.
The page loads once. After that, it's yours.
One Habit Worth Changing
Next time you're about to drag a file into an online tool, any online tool, not just image compressors, pause for three seconds and ask: does this file need to leave my computer to get this done?
For most things, the honest answer is no. Browser technology in 2025 is quietly capable of things that used to require servers. PDF processing, format conversion, document editing, video trimming, tools that run locally are increasingly available for all of these, built by people who got frustrated with the same problem.
For images, the answer has been no for a while. The tool just hadn't been built with a decent interface.
Now it has.
zeropng.com - free, no account, works offline, and the network tab stays silent.
Your photos stay on your computer. That's the whole idea.
Top comments (3)
Client work you were under NDA not to share. Passport scans. Photos of your home, your car, your children. Screenshots that happened to contain your email, your account number, your address. Medical images. None of those images belong in public image compression services. Unless the documents are my own and I decice to do so. Only that there are other situations like using a Google phone camera's "scan document" option or "add to drive" etc.
Thanks for providing an alternative!
This is a really good point that most devs don't think about. I've caught myself dragging client mockups into TinyPNG without a second thought, and yeah, those are technically NDA-covered files going to someone else's server.
The Canvas API + OffscreenCanvas combo has been capable enough for this for a while now. For PNG specifically you can get surprisingly good results with just
canvas.toBlob('image/webp', quality)and then converting back if you need PNG output. The WASM route (like Squoosh uses) gives you even more control — mozjpeg and oxipng running client-side.Curious about one thing though — how are you handling the actual compression? Are you using the browser's built-in canvas encoding or did you bundle something like libsquoosh/WASM? The quality difference between the two approaches can be pretty significant, especially at lower quality settings where canvas encoding tends to produce worse artifacts.
Used upng - small, fast and advanced PNG / APNG encoder and decoder which is the main PNG engine for Photopea image editor