For assistance on https://stackoverflow.com/questions/66071010/how-do-you-send-a-base64-image-to-discord-webhook/

bot.js

const Discord = require('discord.js');
const bot = new Discord.Client();

bot.on('message', async msg => {
    if(msg.author.bot) return;
    if(msg.content === '!test') {
        const Hook = new Discord.WebhookClient("WEBHOOK_ID", "WEBHOOK_TOKEN");
        const image = 'data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/.........'

        const imageStream = new Buffer.from(image.split("base64,")[1],'base64');
        const attachment =  new Discord.MessageAttachment(imageStream);

        const embed = new Discord.MessageEmbed().attachFiles(attachment);

        Hook.send(embed);
    }
}); 

bot.login('DISCORD_TOKEN');