Is masking the duplicated movieclips possible?

1

I ve got a mouse trail, I would like to mask all the trails to a image, is it possible masking the duplicated movieclips (that come as trails) to a image that is below ?? using set mask()?? as for me only the actual movie masks the image but not the duplicated ones, unfortunately. can anyone help plz. below is the code i ve used.

var a:Number=0;

onEnterFrame=function():Void{
a+=1;
duplicateMovieClip(mcAni,“mcAni”+a,a);
[color=red]img.setMask(“mcAni”+a);[/color]
if(a>36){
removeMovieClip(mcAni)
a=0;
}
mcAni._x+=(_xmouse-mcAni._x)/15;
mcAni._y+=(_ymouse-mcAni._y)/15;

}