From iOS 11 onwards, iPhones have saved images in HEIC format by default setting. HEIC — High Efficiency Image Container — is a great format: it generates images with about half the storage of similar JPEGs while maintaining high photo quality.
Yet there is a significant catch. HEIC is an Apple-proprietary format which is not universally accepted away from the Apple ecosystem. Windows PCs, Android devices and many websites do not support HEIC images with no extra apps.
Transforming HEIC to JPG is the critical action making iPhone pictures usable on all devices. Frequent cases needing conversion involve transferring images to non-Apple users, posting pictures to social media incompatible with HEIC.
People with Macs have a simple method. Open the HEIC file here in Preview, navigate to File, then Export and pick JPEG as the output format.
On Windows, online conversion tools handle HEIC to JPG converting with no downloads. Upload the HEIC photo and save the converted JPG.
Use alljpgconverters.com offering a completely free web-based HEIC to JPG tool with no download needed.