Hi Paul,
You could use Windows Explorer to add metadata to the files (assuming they are JPG). You can right click on an image, got to Properties -> Details. Here you can add keywords to "Title", "Tags", "Comments" fields. You could use words like "Qantas", "B738", "VH-XXX", "Special Livery" etc in the Tags area. These words become searchable in Windows. I assume MAC would have a similar option as its common to JPG files to have metadata attached I am just not sure of the MAC process.
Capture.jpg
I personally use Photoshop Lightroom (I use it for other photography reasons too), because you can also add GPS co-ordinates to the photos by use of Google maps by placing photos on the map. It can do really good categories and searching options. Lightroom also works with attaching metadata to RAW files which I take most of my photos in.
But.. first option is free, Lightroom will cost.
Hope that helps.