The Windows icon and favicon container — the one image format built to hold several sizes of the same picture at once.
ICO is the file format Windows uses for application icons, shortcut icons, and the classic favicon.ico that browsers look for in a website's root folder. Unlike a normal image file, a single ICO can bundle several sizes of the same picture — 16×16, 32×32, 256×256, and others — inside one container, so an operating system or browser can pick whichever size fits a taskbar, a desktop, or a browser tab without scaling a single image up or down. That structure is also what makes ICO awkward to create by hand: almost no one designs directly in ICO, they design a square logo as a PNG and then need something to package it into the multi-size container Windows and browsers expect. The format has stayed relevant well past its Windows-only origins because the web adopted the same favicon.ico convention decades ago and never fully replaced it, even though PNG favicons are now also common. Anyone handed a design brief that calls for a favicon or a Windows icon is really being asked for an ICO file, not the PNG they probably already have.
iPhone, iPad, and Mac open ICO files as static images in Photos and Preview, though they display only the largest embedded size rather than the full multi-size set. Windows uses ICO natively for icons and shortcuts. Most web browsers do not display an ICO file directly, only through its use as a site's favicon.
Web servers and Windows both look specifically for an ICO file to represent a site or an app, and a plain PNG does not fill that role no matter how it is named. Converting on-device turns a finished logo into the exact container format those systems expect.
Filemorph can convert ICO to PNG on-device — extracting a usable image out of an icon file, or the reverse for building one.
Filemorph converts .ico files entirely on-device on iPhone, iPad and Mac — no upload, no account, and it works in Airplane Mode.
Relevant operations in Filemorph:
ICO is the format behind Windows application and shortcut icons and the classic favicon.ico a website places in its root folder so browsers show it in the tab and bookmarks. It's built to hold multiple icon sizes in one file rather than a single image.
Start with a square PNG of your logo — 256 by 256 pixels is a safe size — and convert it to ICO. Filemorph packages the PNG into a valid .ico file directly on the iPhone, ready to use as a favicon or a Windows icon.
Yes. PNG to ICO is in Filemorph's free tier, including small batches, and the conversion runs on-device — a brand asset never has to be uploaded to a website to become a favicon.