PNGs and stroke order GIFs of most kanji.
The files are named with the unicode code point of the character in hex. For example you can get the png file name for 犬 like this in JavaScript:
const fileName = '犬'.codePointAt(0).toString(16) + '.png';
The gifs were generated using Kanimaji which uses KanjiVG. You can use those if you want different resolutions, colors, etc.
The pngs were generated using node-canvas. I think the font is Meiryo, I don't remember.