Windows tells you it cannot open an iPhone photo, or the Photos app offers an extension you never meant to install. The file is almost always a HEIC. Since iOS 11 the iPhone camera has saved stills in that container, because it keeps more pictures in the same storage. A PC that has never been taught to read HEIF looks at those bytes and stops.
The picture is not corrupt merely because Windows shrugs. The Photos app on the iPhone, and Preview on a Mac, open it because Apple ships the decoder. Windows does not, unless the HEIF Image Extensions are installed and, for some files, the HEVC video extension from the Microsoft Store as well. Those add-ons teach that particular PC to display HEIC. They are the right choice when the laptop itself should understand the camera roll: a local album, a drive of originals, a habit of keeping HEIC.
They do nothing for the person on the other side of an email. A school form, an insurer, a client, or a family laptop will not install an extension just to see one birthday photo. They need a file their computer already opens. That file is a JPG. Changing photo.heic to photo.jpg does not convert anything. The bytes are still HEIC, and the next machine fails in the same way, sometimes with a stranger error because the extension now lies about the contents.
When a JPG is the simpler file
Use a browser conversion when the photo has to travel. On the Windows PC or on the iPhone, open a page that decodes the HEIC locally and downloads a JPG. Leave the original on the phone if you still want Apple's copy. Attach the JPG to the mail, the form, or the chat.
Chrome, Edge, and Firefox on that same Windows PC can do the conversion even while the Photos app still cannot open the HEIC. You do not have to repair Windows first. Make a JPG, then open that JPG in Photos, mail, or a document. If a chat app already delivered a JPEG, check the extension before you convert anything: a real iPhone original ends in .heic or .heif.
You can [convert HEIC to JPG in the browser](/) without sending the picture to a server. The download is a new JPEG. It will often be larger than the HEIC, and it will not include the GPS pin or the camera EXIF block. That is the right trade when the task is simply that someone can open the picture. It is the wrong file when a print lab asked for the untouched original and a Mac can export it with the color profile still attached.
Live Photos and very large shots
A Live Photo is a still plus a short movie. A JPG conversion keeps the still. The press-and-hold video is not inside that JPG. Export the video from the Photos app if the motion is the thing you needed.
A 48-megapixel iPhone photo is modest as a HEIC and heavy once it is decoded to pixels. Convert those one at a time, and close other tabs if the browser complains about memory. The result is still a normal JPG that Windows can open.
If this PC is yours and you will open HEIC every week, install the HEIF extension and keep the originals. If you are handing a picture to someone who will not install anything, send the JPG.