一种强力方法是简单地将两个图像都作为BufferedImage对象加载，然后逐个像素地遍历“主”图像，看看是否可以在其中找到“子图像”。
我已经实现了这一点前一段时间，并将张贴下面的代码作为一个MCVE。
但是注意：当你把图像保存为JPG文件时，它们会被压缩，而这种压缩是 * 有损 * 的。这意味着像素不会有完全相同的颜色，即使它们在屏幕上是相等的。在下面的例子中，这个问题实际上得到了解决，用一个“阈值”来定义像素可能有多大的不同。但这有点武断，不那么可靠。（更强大的解决方案需要更多的努力）。
我强烈建议将图片保存为PNG文件。它们使用无损压缩。所以对于PNG文件，你可以在下面的代码中设置threshold=0。

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Point;
import java.awt.image.BufferedImage;
import java.net.URL;
import java.util.function.IntBinaryOperator;

import javax.imageio.ImageIO;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class FindImageInImage
{
    public static void main(String[] args) throws Exception
    {
        BufferedImage mainImage = 
            ImageIO.read(new URL("https://i.stack.imgur.com/rEouF.jpg"));
        BufferedImage subImage = 
            ImageIO.read(new URL("https://i.stack.imgur.com/wISyn.jpg"));

        int threshold = 100;
        Point location = findImageLocation(
            mainImage, subImage, threshold);
        System.out.println("At " + location);

        SwingUtilities.invokeLater(() -> showIt(mainImage, subImage, location));
    }

    private static void showIt(
        BufferedImage mainImage, BufferedImage subImage, Point location)
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        f.getContentPane().add(new JPanel()
        {
            @Override
            protected void paintComponent(Graphics g)
            {
                super.paintComponent(g);
                g.drawImage(mainImage, 0, 0, null);
                if (location != null)
                {
                    g.setColor(Color.RED);
                    g.drawRect(location.x, location.y, 
                        subImage.getWidth(), subImage.getHeight());
                }
            }
        });
        f.setSize(1500, 800);
        f.setLocationRelativeTo(null);
        f.setVisible(true);
    }

    static Point findImageLocation(
        BufferedImage mainImage, 
        BufferedImage subImage, 
        int threshold)
    {
        return findImageLocation(mainImage, subImage, (rgb0, rgb1) -> 
        {
            int difference = computeDifference(rgb0, rgb1);
            if (difference > threshold)
            {
                return 1;
            }
            return 0;
        });
    }

    private static int computeDifference(int rgb0, int rgb1)
    {
        int r0 = (rgb0 & 0x00FF0000) >> 16;
        int g0 = (rgb0 & 0x0000FF00) >> 8;
        int b0 = (rgb0 & 0x000000FF);

        int r1 = (rgb1 & 0x00FF0000) >> 16;
        int g1 = (rgb1 & 0x0000FF00) >> 8;
        int b1 = (rgb1 & 0x000000FF);

        int dr = Math.abs(r0 - r1);
        int dg = Math.abs(g0 - g1);
        int db = Math.abs(b0 - b1);

        return dr + dg + db;
    }

    static Point findImageLocation(
        BufferedImage mainImage, 
        BufferedImage subImage, 
        IntBinaryOperator rgbComparator)
    {
        int w = mainImage.getWidth();
        int h = mainImage.getHeight();
        for (int x=0; x < w; x++)
        {
            for (int y = 0; y < h; y++)
            {
                if (isSubImageAt(mainImage, x, y, subImage, rgbComparator))
                {
                    return new Point(x, y);
                }
            }
        }
        return null;
    }

    static boolean isSubImageAt(
        BufferedImage mainImage, int x, int y, 
        BufferedImage subImage, 
        IntBinaryOperator rgbComparator)
    {
        int w = subImage.getWidth(); 
        int h = subImage.getHeight();
        if (x + w > mainImage.getWidth())
        {
            return false;
        }
        if (y + h > mainImage.getHeight())
        {
            return false;
        }
        for (int ix=0; ix < w; ix++)
        {
            for (int iy = 0; iy < h; iy++)
            {
                int mainRgb = mainImage.getRGB(x + ix, y + iy);
                int subRgb = subImage.getRGB(ix, iy);
                if (rgbComparator.applyAsInt(mainRgb, subRgb) != 0)
                {
                    return false;
                }
            }
        }
        return true;
    }

}