Is WebP really better than JPEG?
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.

[1] https://bellard.org/bpg/