What is the most efficient way to add X amount of blank canvas to the top of a bunch of images? I'm sure there's a program capable of doing a batch process somewhere. But so far all I've found is batch programs that will resize all canvases to the same size; I don't want that, as in this case all images are different dimensions. I have access to GIMP ifranView and Photoshop, though I'd have to dig out my Photoshop CD and reinstall it.
Dig out that Photoshop CD, which includes Adobe Bridge if it's CS or later, or set up a free trial of Creative Cloud and download Photoshop. This is really easy to do.