In CompizConfig Settings Manager you can activate the plugin
Enable Window Previews, which doesn't show previews for minimized windows. (When I first checked this, I saw previews - but now I can't reproduce it. Seems to be buggy.)
Previews for windows on other workspaces are optional; activate them by unchecking
Taskbar Shows Only Windows of Current Viewport.
Compiz Wiki says: "The Window Previews displays a small thumbnail of any displayed (not minimized) window when you hover over it's button in your desktop environment's window list."
But always keep in mind: CCSM is an advanced tool. Use with caution. This tool allows you to deeply configure Compiz's settings. Some options may be incompatible with each other. Unless used with care, it is possible to be left with an unusable desktop.