How compression works here
Images are decoded with createImageBitmap, optionally scaled to a maximum long edge, then re-encoded through Canvas toBlob. JPEG quality is the slider you set. PNG input at very high quality stays PNG; otherwise photographs are written as JPEG because that is where the size win is. Compress image online, compress JPEG online, compress WebP, or use it as a JPEG compressor, PNG compressor, image size reducer or photo size reducer — same pipeline.
Nothing is uploaded. Compress images without uploading: close the tab and the files are gone. That is how you reduce JPG file size, reduce PNG file size, or reduce image file size on a confidential photo. Batch drop several images and download each result. For a QR of a compressed asset URL, use the QR generator.