By default, Opera browser shows tab previews or thumbnails in taskbar on Windows 7. This feature is although useful but can be annoying, if you have lot many tabs opened in Opera. Below is an easy way to disable it.
Turn off Opera tab previews shown in Windows 7 taskbar:
Open Opera, type opera:config in address bar and open it. Navigate to User Prefs > expand it and search for ‘Use Windows 7 Taskbar Thumbnails’. Uncheck its box and Save.
You may need to restart Opera for letting changes to take effect. Now you will see only a single preview of the active tab running in Opera.