Enlarge the size of PNGs by repeatedly writing a string to metadata

png_increase.mjs

import png from 'png-metadata';
import fs from 'fs';

const desiredSize = 24000;
const folder = './assets/';
const creatorString = 'Skeleton Crew';
const fillerString = 'https://treattoolbox.com ';

const bumpImageSize = async (file) => {
    if (file.endsWith('.png')) {
        const filePath = folder + file;

        let fileSize = (await fs.promises.stat(filePath)).size;

        if (fileSize <= desiredSize) {
            console.log('bumping ' + filePath);

            // load from file
            let s = png.readFileSync(filePath);
            // split
            let list = png.splitChunk(s);
            // append
            let iend = list.pop(); // remove IEND

            const creatorSize = getBytes(creatorString);

            let creatorChunk = png.createChunk('aaAa', creatorString);
            list.push(creatorChunk);
            fileSize += creatorSize;

            let fillingString = '';

            while (fileSize + getBytes(fillingString) <= desiredSize) {
                // const fillingSize = getBytes(fillingString);
                fillingString += fillerString;
            }

            let fillingChunk = png.createChunk('aaAb', fillingString)

            list.push(fillingChunk);
            list.push(iend);

            // join and save
            let newpng = png.joinChunk(list);
            fs.writeFileSync(filePath, newpng, 'binary');
        }
    }
}

function getBytes(string) {
    return Buffer.byteLength(string, 'utf8')
}

fs.readdirSync(folder).forEach(file => bumpImageSize(file));

First run:
npm i --global png-metadata
then:
node png_increase.mjs
and there should be a directory in the same location as the script that contains all your images and metadata named assets