Google always tries to make the web faster, Google says all image formats exists today such as JPEG,PNG ,GIF etc are established over decade ago with technology available at that time, Google feels there is a need for new image format for the web by compressing lossy images like JPEG and still preserving the quality and resolution, hence the evolution of Google’s new image format, WebP.
Launch of WebP is to significantly reduce the byte size of photos on the web, allowing websites to load faster than web before.
According to Google they re-encoded over 1,000,000 images (mostly JPEG and some PNG and GIFs) to WebP format, they found WebP images size on average 39% is less than original images.
Google released a conversion tool to convert images to WebP format, at present browsers not support WebP image format.Conversion tool supports Linux x84 (64-bit) only, support for windows will be added later.
Maximum size of WebP image is 16383*16383 pixels.You can view the comparison between JPEG and WebP images here.
You can find more details on Chromium blog and on WebP page.