I wonder, why nobody mentioned Patrice Bellard's BPG[1]. It is based on HEVC and can be supported in any browser via a Javascript. From his website:
BPG (Better Portable Graphics) is a new image format. Its purpose is to replace the JPEG image format when
quality or file size is an issue. Its main advantages are:
* High compression ratio. Files are much smaller than JPEG for similar quality.
* Supported by most Web browsers with a small Javascript decoder (gzipped size: 56 KB).
* Based on a subset of the HEVC open video compression standard.
* Supports the same chroma formats as JPEG (grayscale, YCbCr 4:2:0, 4:2:2, 4:4:4) to reduce the losses during the
conversion. An alpha channel is supported. The RGB, YCgCo and CMYK color spaces are also supported.
* Native support of 8 to 14 bits per channel for a higher dynamic range.
* Lossless compression is supported.
* Various metadata (such as EXIF, ICC profile, XMP) can be included.
* Animation support.
