HEIC is the format iPhones have used for photos since iOS 11. It stores an image at roughly half the size of a JPG of similar quality, which is why Apple chose it, but plenty of software still cannot open it: older Windows installs, many web upload forms, print shops and some photo editors. This page opens with JPG already selected as the output, so you only drop the photos and convert. Safari can read HEIC on its own; in Chrome, Edge and Firefox a HEIC decoder loads the first time you add a photo, and from then on everything runs on your device without an upload. Expect the JPG to be larger than the HEIC it came from, often by half again or more, because JPG is a less efficient format. The quality slider controls that tradeoff, and 85 to 92 keeps a phone photo visually identical. The output also loses its EXIF data, including the GPS position recorded by the camera, which is useful before posting a photo publicly. If you would rather stop the iPhone producing HEIC at all, set Settings, Camera, Formats to Most Compatible. For a lossless copy use HEIC to PNG Converter, and to shrink the JPGs further use Image Compressor.
Choosing the right image format for web use has a significant impact on file size and quality. JPEG (Joint Photographic Experts Group) uses lossy compression optimized for photographs: it discards subtle color gradients in ways the human eye does not easily notice, achieving compression ratios of 10:1 to 20:1 at acceptable quality. PNG (Portable Network Graphics) uses lossless compression and supports full transparency (alpha channel), making it ideal for logos, icons, screenshots, and images with sharp edges or text. WebP is Google's modern format that achieves better compression than both JPEG and PNG at equivalent quality: typically 25 to 35 percent smaller than JPEG at the same quality setting, and 26 percent smaller than PNG for lossless images. WebP also supports transparency like PNG. GIF (Graphics Interchange Format) is the oldest format still in use, primarily kept alive by its support for animation. For still images, GIF is inferior to PNG in both quality and compression, limited to 256 colors per frame. Converting to WebP for web delivery is the most impactful single optimization for image-heavy sites. Browser support for WebP is now essentially universal (Chrome, Firefox, Safari 14+, Edge). For cases where legacy Safari support is required, serving WebP via a picture element with a JPEG fallback provides the best result across all browsers.