There's an old locked thread about adding WebP support to GIMP.
Here ---> http://ubuntuforums.org/showthread.p...highlight=webp
That PPA hasn't been updated for ages, but the 12.04 Precise version seems to work OK with 14.04 Trusty.
I've created a deb file from the old PPA.
It's in the attachment below.
Download and untar it first.
Install the deb
sudo apt-get update; sudo apt-get -y install libwebp-dev
Then with GIMP it will be possible to import and export webp files.
sudo dpkg -i gimp-webp_0.2-1.deb
This works OK for me with 32 bit system.
I don't have access to a 64 bit system, but maybe somebody else can test it and leave feedback.