After a search for batch resizing tools, which most require a bit of fiddling around with. I found a handy command line tool which comes with maverick, sips.
If you run the above in a directory of pictures, it will resize all pictures in the current directory.
For my needs, I passed
-Z to keep the ratio, and a maximum height of 1024 pixels.
As always, make sure to keep the original in case you don’t like the results!