If the webpage declares that it wants JPEGs or PNGs, but not HEICs, Safari will transparently convert the file before the webpage sees it.
<input type="file" accept="image/jpeg" />
<input type="file" accept="image/jpeg" />
iOS supports HEIF, Safari does not.
Why Safari does not, still, 5 years later, I can't tell you.
The Apple employees who work on WebKit, Safari's open source browser engine, or even those who make Safari from WebKit are not the same Apple employees who work on iOS's file system or Photos.app or anything else found on an iPhone when you first take it out of the box.
Still, it is odd that iOS 16, including Safari, has added support for AVIF but HEIF still doesn't work in Safari.
Your argumentative tone would've made sense if my criticism was directed at the Safari team for not implementing HEIF support. But my criticism is towards Apple for failing to make a cohesive product.
Exactly. Safari had the motivation/resources to add AVIF support, but not HEIF. So it seems like Apple chose to back the wrong horse (HEIC) at first and is now pivoting to AVIF