I use imagemagick to split spritesheets into single images for games that I make[0]. More than 1 gamedev has saved countless of hours thanks to it, so I 100% hope it never breaks.
[0]: https://gist.github.com/ldd/9b576bb6f0ac99a0a7895eaf1aae7802
[0]: https://gist.github.com/ldd/9b576bb6f0ac99a0a7895eaf1aae7802
Netpbm also does this; you can use the "pamdice" program (together with "pngtopnm" and "pnmtopng" to decode and encode PNG). However, pamdice requires creating intermediate files, while ff-dice doesn't require that.
So, you have two more things to try if ImageMagick won't work.
Ironically, trying to good for `ff-dice` or `pngff` sends me back to this thread!
(Although there are a lot of files, you will only need to compile the files that you need, and you can delete the files that you don't need.)