Drop an image, get a JPEG with 600 DPI written in its header — plus exact pixel dimensions and file size if you need them. Nothing is uploaded; it all runs in your browser.
600 DPI shows up in specs for document and signature scans — the idea being a fine-detail scan of something physical. In a digital file, though, DPI is a header label: it records “treat 600 pixels as one inch” for print-size arithmetic and changes nothing about the pixels themselves. This page writes 600 into your JPEG’s JFIF density field, and can meet exact pixel dimensions and an exact file size at the same time, entirely in your browser.
Worth saying plainly: if a spec wants a 600-DPI scan of a signature, the detail has to come from the scanner or camera. Relabelling a small, soft image as 600 DPI doesn’t add information — and a checker that looks at actual pixel dimensions will see through it. What the label legitimately does is record the scan resolution so software that auto-sizes images (word processors, layout tools, print kiosks) places the image at the right physical size. The arithmetic: at 600 DPI, 3.5×1.5 cm is roughly 827×354 px — so a genuine 600-DPI signature scan of that box should be around that size. Scan at or above it, then use this page for the exact pixels, bytes and label.
Several photo-resizer sites sell “600 DPI” versions of visa and exam photos where the official source names no such figure — the number is usually a projection from a paper-photo size, not anything the portal checks. When a form you’re filling names a DPI, use it; when a third-party guide does, check the official source (our verified requirements table links them). Most upload portals validate pixels and bytes — the 200 and 300 DPI pages cover the figures forms actually name. The re-encode here strips GPS/EXIF as a side effect, which for anything you upload is worth having — or, when you have a genuine 600-DPI scan that just lacks the label, the label-only button with the result writes it into the original JPEG’s header (JFIF density plus existing EXIF resolution tags) without re-encoding or touching a single pixel.