making an alpha channel cast shadows.?

Hi , i have an image of a mirror , the foto had a wall in the back , so i used photoshop to add a mask to it so that only the mirror would appear , this is done.

But now , i want it to not cast shadows , or even better , if it can cast the shadows of only the mirror part , the part that is visible because of the alpha ,

right now , ya can see a black plane as a shadow ,

Any suggestions ?

I’m not sure exactly what you’re asking, but I think you want to look at the materials settings for the object receiving the shadow, and turn on the TraShad button. Only the non-transparent parts of the plane will cast shadows on the object.