Hi there, thanks for the dimensions, @Testuo Shima

The GBC cover collection I have found has turned out a little more annoying to work with than it seemed at first.
A simple resize didn't work as the ratios between the spines and covers were different. Thankfully I have been able to batch process the covers, creating separate cropped spines and covers, resizing them and finally merging them back together.
Re-combining I thought would be simple, but the tools I had couldn't seem to do it! At last I found some software that could do it in batch also
On a different note, there are also some excellent game title logos, (I think complete) on the hyperspin site.
I also found some software called imagemagick, I can't figure out how to use it, however someone skilled could auto batch combine the aforementioned Game Title logos, (which have transparency) Game Title Images and or Snaps, along with a background Fill, with the required dimensions to "automagically" generate 600+ box backs. Which would be awesome!