What you see
You choose a photo and the tool says “That image could not be decoded. It may be corrupt or in an unsupported format.” The photo opens fine on your iPhone, so it is not damaged.
Why it happens
Since iOS 11, iPhones save photos as HEIC rather than JPEG, because HEIC files are about half the size for the same quality. The image tools here read your photo with the browser’s own image decoder, and that is where HEIC falls down: Safari can usually open it, but Chrome, Edge and Firefox cannot.
Picking a photo straight from the Photos library in Safari on an iPhone often works, because iOS hands the page a JPEG copy. The problem shows up most with HEIC files that have been copied to a computer, sent by email or synced to a cloud drive.
What to do
- Convert it first. The HEIC to JPG Converter turns a HEIC or HEIF photo into a JPEG, PNG or WebP in your browser, and the result opens in every other tool. Your photo is not uploaded.
- Change what the iPhone saves. In Settings, Camera, Formats, choose Most Compatible, and new photos are saved as JPEG. They take roughly twice the space on the phone.
- Use Safari. On a Mac or an iPhone, Safari can often open the HEIC photo in the tool directly.