I've been tasked with changing some photos from landscape orientation to portrait for a photo frame. The photos are only going to be printed 6x4 but there is no room at the edges to crop, so am just going to add black borders top and bottom. What is the best way to achieve this? I have available Paint.Net and Lightroom 4. I was thinking of just creating a new canvas in Paint.Net at the size I want, and then adding the photo as a new layer and resizing to the dimensions needed. Is this the best way, or is there a better way to do it?