Remove Hidden Data from ICO Icon Files
12 A format built to hold several images at once, not one photo
ICO is what Windows uses for app icons and what browsers use for favicons - and unlike every other
format on this site, a single .ico file is genuinely a small container that can hold
several versions of the same image at different sizes and color depths (16×16, 32×32, 256×256, and so
on), so the operating system can pick whichever one fits the context. There's essentially no metadata
standard for ICO the way EXIF exists for JPEG - no GPS, no camera info, nothing like that ever ends up
in one. The realistic risk here is closer to the structural, "don't trust the bytes" category than the
privacy category this site covers for camera photos.
Go deeper: the one thing ICO looks nearly identical to, on purpose treated differently
ICO's file signature is 4 bytes: 00 00 01 00. Change exactly one of those bytes -
00 00 02 00 - and you have a CUR file instead: Windows' format for animated cursors,
which reuses almost the entire ICO container structure with a different "type" field and an extra
hotspot coordinate per image. This tool deliberately recognizes only the ICO signature and treats
a CUR file as unrecognized rather than guessing that "it's basically the same thing" - the same
principle behind refusing to trust a file extension anywhere else on this site. Multiple embedded
icon sizes inside a single valid ICO file are all decoded and accounted for; only the first,
largest suitable image is carried through the sanitize pipeline, which is why a multi-size ICO in
always comes back as a single plain image out.
Where an ICO's real risk usually sits
Because ICO shows up most often as a favicon quietly sitting on a website, or an icon bundled inside software you downloaded, the more realistic threat model is the same one covered on the comparison page for structural attacks in general - a malformed or deliberately crafted container tricking a careless parser - rather than a metadata leak from a camera. Decoding fully to raw pixels and rebuilding from scratch, the same guarantee this tool applies to every format, removes that risk category regardless of what an ICO file's internal structure happened to claim about itself.