try
{
    Rectangle screen = new Rectangle (Toolkit.getDefaultToolkit().getScreenSize());
    BufferedImage capture = new Robot().createScreenCapture(screen);
    ImageIcon icon = new ImageIcon(capture);
    int len = icon.getWidth();
    ImageIO.write(capture, "jpg", new File("screenshot.jpg"));
    
    try {
        Class.forName("com.mysql.jdbc.Driver");
    } catch (ClassNotFoundException ex) {
        Logger.getLogger(Sign_up.class.getName()).log(Level.SEVERE, null, ex);
    }
    
    try (Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/webapp", "root", "")) {
        Statement at = con.createStatement();
        String qt = "insert into picture (Pictures) values (?)";
        PreparedStatement pstmt = con.prepareStatement(qt);
        pstmt.setBinaryStream(icon, ...);
    }
}

import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import javax.imageio.ImageIO;
public class ScreenShot {
    public static void main(String[] args) throws Exception {
        if (args.length != 3) {
            // Note: Don't pass passwords on the command line in real life.
            System.err.println("Usage: java ScreenShot <dbUrl> <dbUser> <dbPwd>");
            return;
        }
        // Capture the screenshot
        Rectangle screen = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize());
        BufferedImage capture = new Robot().createScreenCapture(screen);
        
        // Write it to a ByteArrayOutputStream
        ByteArrayOutputStream baos = new ByteArrayOutputStream();
        ImageIO.write(capture, "jpg", baos);
        
        // Insert the bytes into the database
        Connection connection = DriverManager.getConnection(args[0], args[1], args[2]);
        String sql = "insert into picture (Pictures) values (?)";
        PreparedStatement ps = connection.prepareStatement(sql);
        ps.setBinaryStream (1,new ByteArrayInputStream(baos.toByteArray()));
        ps.execute();
        
        // Select the image from the database.
        sql = "select Pictures from picture where id = 1";
        ps = connection.prepareStatement(sql);
        ResultSet rs = ps.executeQuery(sql);
        if (rs.next()) {
            InputStream input = rs.getBinaryStream(1);
            // Write the image to a file (for verification).
            FileOutputStream fos = new FileOutputStream("screenshot.jpg");
            byte[] buffer = new byte[1024];
            while (input.read(buffer) > 0) {
                fos.write(buffer);
            }
            input.close();
            fos.close();
        }
    }
}

CREATE TABLE test.picture (
    id int AUTO_INCREMENT ,
    Pictures MEDIUMBLOB,
PRIMARY KEY (id)
);