Answer
How do I check whether a photo has metadata?
File properties on Windows or Get Info on macOS will show you the basics. A dedicated viewer shows the fields those summaries leave out — which is most of them.
Updated
The built-in route works and is worth knowing. On Windows, right-click the file, open Properties and look at the Details tab. On macOS, open the image in Preview and show the inspector. On Android and iOS, the photo details panel exposes a subset, usually including a map if coordinates are present.
These summaries are curated, though, and the curation is the problem. They show camera, date and dimensions because that is what most people want. They generally do not show the XMP packet, the IPTC block, the embedded thumbnail, the maker note — the vendor-specific section where camera manufacturers record lens serial numbers, shutter counts and focus data — or C2PA content credentials. A file can look nearly empty in Properties and still be carrying several kilobytes of hidden text.
A dedicated viewer reads all of it. The EXIF viewer here parses the file in your browser and lists every field it finds, grouped by where in the file it was stored, and it never uploads anything — you can confirm that by disconnecting from the network and watching it keep working.
The case worth checking deliberately is AI-generated PNGs. Tools in the Stable Diffusion family write the complete prompt, negative prompt, seed, sampler, CFG scale and model hash into a text chunk, and none of that appears in any operating system summary. It is readable in a plain text editor if you know where to look, and invisible everywhere else.
More on this: EXIF viewer, Metadata remover.
Terms used here: EXIF, IPTC, XMP, C2PA.