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.
Record an Action in Photoshop that adds a relative amount (percentage, pixels, inches, whatever) to the top of the canvas. Any of the images you'll be modifying will do. Then either:
In Bridge, select all the images you want to modify. From
Tools > Photoshop > Batch... select the action you recorded, to be performed on each selected image.
In Photoshop choose
File > Automate > Batch..., which gives you the same dialog. You'll have to browse to select the images.
Run the batch.