I noticed that it seems like Luarocks did not pick up the new version: https://luarocks.org/modules/3rd/image.nvim
Nixpkgs is also stuck at 1.3.0: https://search.nixos.org/packages?channel=unstable&show=vimPlugins.image-nvim&query=image-nvim
I'm not sure but maybe the nix updater picks up versions from Luarocks and that's why it's not updated. Is it intentional that a new version is not published there?