[Java] 產生驗證碼圖片

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.util.Random;

import javax.imageio.ImageIO;

public class TestCaptchaImage {

    public static void main(String[] args) throws Exception {
        String captcha = "09875";

        int width = 55;
        int height = 20;
        Color fontColor = new Color(36, 85, 92); /*文字顏色*/
        Color lineColor = new Color(65, 161, 175); /*線條顏色*/
        Color bgColor = new Color(208, 226, 229); /*底色*/

        Random random = new Random();
        random.setSeed(System.currentTimeMillis());

        BufferedImage image = new BufferedImage(
            width, height, BufferedImage.TYPE_INT_RGB
        );
        Graphics g = image.getGraphics();

        /* 底色 */
        g.setColor(bgColor);
        g.fillRect(0, 0, width, height);

        /* 畫線 */
        g.setColor(lineColor);
        for (int i=0; i < 20; i++) {
            g.drawLine(
                random.nextInt(width), 0,
                random.nextInt(width), height
            );
        }

        /* 畫出文字 */
        g.setFont(new Font("Atlantic Inline", Font.BOLD, 20));
        g.setColor(fontColor);
        g.drawString(captcha, 0, 18);

        /* 畫線 */
        g.setColor(lineColor);
        for (int i=0; i < 4; i++) {
            g.drawLine(
                0, random.nextInt(height),
                width, random.nextInt(height)
            );
        }

        g.dispose();

        ImageIO.write(image, "png", new File("captcha_image.png"));
    }
}

參考文件：
Graphics (Java 2 Platform SE 6)