How JustCompressImages Works
Your images are processed entirely in your browser. Here is exactly what happens under the hood.
Browser-Side Processing
JustCompressImages runs entirely in your web browser. When you compress an image, every step happens on your device — no file is ever sent to any server, and no external service processes your data.
Technical Implementation
The tool is built on these browser APIs and open-source libraries:
Canvas API
Your browser's built-in image rendering surface. Images are drawn onto an off-screen canvas element and re-encoded at the quality level you select. This is a native browser capability — no plugins or extensions required.
browser-image-compression
An open-source JavaScript library that orchestrates the compression pipeline, handles large files memory-efficiently, and delegates work to Web Workers.
Web Workers
Background threads that run compression without blocking the browser UI. The page stays fully responsive while images are being processed.
File API and Blob URLs
Files you select are read directly into browser memory. Compressed results are created as Blob objects and offered as downloads. No network request is made at any point.
JSZip
An open-source library used to package batch downloads into a single ZIP file, entirely within the browser.
What This Means for Your Privacy
- Your files are never uploaded to any server
- No third party receives or processes your images
- We have no access to the content of your files
- No image data is logged or stored anywhere
- Files exist only in your browser's memory during processing
How to Verify
You do not have to take our word for it. Here is how to confirm:
- 1 Open your browser's developer tools (press F12, or right-click and choose Inspect)
- 2 Go to the Network tab
- 3 Use the tool to compress an image
- 4 Observe: no outbound requests contain your image data
Alternatively, disconnect from the internet after the page loads. The tool continues to work — because it requires no server.
Trade-offs and Limitations
Because processing happens on your device, performance depends on your hardware. Very large images or large batches may compress more slowly on older or low-memory devices than server-based tools. The tool automatically adjusts file size limits based on your device's detected memory.