A sample GIST in response to https://twitter.com/sjimenezmateo/status/283907731214176256

gistfile1.java

package com.marimon.proof.image.manipulation;
 
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
 
import javax.imageio.ImageIO;
 
public class ImageReaderWriter {
 
    public static void main(final String[] args) throws IOException {
        BufferedImage read =
            ImageIO.read(ImageReaderWriter.class
                .getResourceAsStream("/cow.jpg"));
        Graphics2D graphics = read.createGraphics();
        graphics.setColor(Color.RED);
        graphics.drawRect(10, 10, 100, 100);
        ImageIO.write(read, "png", new File("./target/out.png"));
    }
 
}