I think it would be great if webp was supported for thumbs.

It could override the original format for display. So if someone adds [[File:Foo.png|200px]] and the header accepts webp then 200px-Foo.webp is displayed instead of the jpg.

The images are smaller or same size but almost without artifacts.
Various formats are thinkable:

• JPEG > WEBP
• PNG transparent > WEBP (See http://jsfiddle.net/rbdo0ex8/ from http://upload.wikimedia.org/wikipedia/commons/b/bb/Gorgosaurus_BW_transparent.png)
• PNG 24 > WEBP
• PNG 8? SVG?

With overriding png thumbs this also solves an old problem with PNG images being converted to much larger PNG24 files by ImageMagick.