1.首先需要一个读取ico的jar，链接：https://download.csdn.net/download/airyearth/13218304，

   详细demo代码请见 https://blog.csdn.net/airyearth/article/details/110480949

2.读取出来的文件为Image格式还需要可以转为BufferedImage，以备平均哈希算法（相似图片搜索）使用

3.代码读取ico文件：

InputStream in = new FileInputStream("D:\\tmall.ico") ;
ICOFile ico = new ICOFile(in);
java.util.List list = ico.getImages();
Image image = null;
if (!list.isEmpty()) {
    image = (Image) list.get(0);
}

4.转为BufferedImage：

public static BufferedImage toBufferedImage(Image image) {
    if (image instanceof BufferedImage) { return (BufferedImage) image; }

    image = new ImageIcon(image).getImage();

    boolean hasAlpha = false;

    BufferedImage bimage = null;

    GraphicsEnvironment ge = GraphicsEnvironment.getLocalGraphicsEnvironment();

    try {

        int transparency = Transparency.OPAQUE;

        if (hasAlpha) { transparency = Transparency.BITMASK; }

        GraphicsDevice gs = ge.getDefaultScreenDevice();

        GraphicsConfiguration gc = gs.getDefaultConfiguration();

        bimage = gc.createCompatibleImage(image.getWidth(null),

                image.getHeight(null), transparency);

    } catch (HeadlessException e) {

    }

    if (bimage == null) {

        int type = BufferedImage.TYPE_INT_RGB;

        if (hasAlpha) { type = BufferedImage.TYPE_INT_ARGB; }

        bimage = new BufferedImage(image.getWidth(null),image.getHeight(null), type);

    }

    Graphics g = bimage.createGraphics();

    g.drawImage(image, 0, 0, null);

    g.dispose();

    return bimage;

}

5.平均哈希算法：

private static byte[] hashValue(BufferedImage src){
    BufferedImage hashImage = resize(src,HASH_SIZE,HASH_SIZE);
    byte[] matrixGray = (byte[]) toGray(hashImage).getData().getDataElements(0, 0, HASH_SIZE, HASH_SIZE, null);
    return  binaryzation(matrixGray);
}

6.相似度比较：

private static float compare(byte[] f1,byte[] f2){
    if(f1.length!=f2.length)
        throw new IllegalArgumentException("mismatch FingerPrint length");
    int sameCount=0;
    for(int i=0;i<f1.length;++i){
        if(f1[i]==f2[i])++sameCount;
    }
    return (float)sameCount/f1.length;
}