The Offset merge is a gizmo that allows you to merge multiple frames together and
average them to remove unwanted objects. A great use is to remove wires and rigs from a shot that have a contrasting colour to the background.
Use the slider to determine how many frames you average (the current maximum is 10).
You then have to merge operations, Max & Min. Use Min to remove brighter objects, otherwise Max for darker.
Download the nuke script from the link below.