Merge images

I have a couple of sets of related density plots (each set with ~9 images) that I need to enter into a report. I'm feeling lazy today and don't want to go through the pain of uploading each of these to our internal wiki so I merged them instead.

The montage program (part of the ImageMagick suite of tools) is really simple and effective for this:

Hey presto a set of merged density plots laid out into two columns (regardless of the number of images) with some spacing between them and a bit of drop shadow to visually separate the plots.