XnView Software

Update: libwebp 0.5.2

JFTR, 0.6.0. XnView 2.40 (full ZIP) contains a new Webp plugin, it works for me on Windows 7, where I have the required MSVCR120.dll (2013).

On the XnView plugins download page Webp is still at an older state suited for W2K, The XnView shell extension is apparently still at a state not supporting Webp at all.