WebP

In 2010, Google announced a new image format, WebP (read “weppy”). https://developers.google.com/speed/webp/

More effective than JPEGs, PNGs, and GIFs, YouTube is using it to show YouTube video previews, which speeded up page loading by 10%: http://blog.chromium.org/2014/03/webp-improves-while-rolling-out-across.html

So far, it’s natively supported in Google Chrome, Firefox, Opera, and a few other browsers except Safari.

You can convert images to and from WebP format using the libweb library or the webp and dwebp CLI tools. https://developers.google.com/speed/webp/docs/using

By the way, Telegram transmits regular stickers in this format.