Turn the HEIC photos your iPhone shoots by default into JPG or PNG that opens anywhere. Drop in several at once and set the JPG quality to balance file size against detail. Conversion happens inside your browser, so the photos never leave your device.
Browsers can't decode HEIC on their own, so the first conversion downloads a converter of about 3 MB. After that it comes from cache, with no wait.
It's the high-efficiency image format Apple has used as the iPhone default since iOS 11. It stores the same quality in roughly half the space of a JPG, but Windows, Android and older software often can't open it.
No. The converter runs inside your browser, so the image data never leaves your device.
PNG is lossless, so it barely compresses photographs. JPG will be far smaller. Unless you need transparency or you're converting a screenshot, pick JPG.