Where to store downloaded icon?

["Edward C. Jones" <edcjones@comcast.net>]

I have an up-to-date Debian testing (wheezy), amd64 version, with kde.

I have compiled and installed the old image viewer "xv".  If I find an icon
for xv somewhere, where on my computer do I store it? How do I put it on 
the
panel?  Currently there is a blank icon on the panel.