So, if I understand what you are saying correctly, the bar code I scan in brings up the movie and all available images/versions of it on the right side of my screen.
Normally 1 barcode is associated to only 1 video (in rare cases it's more) and all the videos have only 1 cover. You're not supposed to have to make a choice. My guess is that you're messing with the facing panel though everything happens in the barcode search panel. I suppose the barcode search returns 1 result and adds it automatically, then it adjusts the facing panel so you can see that the video has been correctly added to the "owned videos" box. You're not supposed to select anything (I suppose from the "existing videos" box), the video corresponding to the barcode you've entered has already been added to the "owned videos" box.