[HaBo]

 Bitmap bmp;
        System.Drawing.Graphics gr;
        System.Drawing.Point startingpoint;
        System.Drawing.Size size;
        System.Drawing.Pen stift = new System.Drawing.Pen(Color.Black);
        System.Drawing.SolidBrush mybrush = new SolidBrush(Color.Black);
        System.Drawing.Font drawFont = new Font("Arial", 9, FontStyle.Regular);
        System.Drawing.Pen pen = new Pen(Color.DarkRed,2);
        System.Drawing.SolidBrush myImagebrush = new SolidBrush(Color.Orange);
        System.Drawing.Font drawImageFont = new Font("Arial", 12, FontStyle.Regular);

        bool mouseClick = false;
        int breite;
        int hoehe;

        public Form1()
        {
            InitializeComponent();
            this.pictureBox1.MouseDown += new System.Windows.Forms.MouseEventHandler(this.paint_MouseDown);
            this.pictureBox1.MouseUp += new System.Windows.Forms.MouseEventHandler(this.paint_MouseUp);
            this.pictureBox1.MouseMove += new System.Windows.Forms.MouseEventHandler(this.paint_MouseMove);
           
            bmp = new Bitmap(400, 400);
            pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
            pictureBox1.Image = bmp;
            gr = Graphics.FromImage(bmp);
            // Name des Mitarbeiter mit einzeichnen
            gr.DrawString("Blas Blaa", drawFont, mybrush, 0, 0);

            pictureBox1.Refresh();
        }

        private void paint_MouseDown(object sender, MouseEventArgs e)
        {
            mouseClick = true;
            size = new System.Drawing.Size();
            startingpoint = new System.Drawing.Point();
            startingpoint = MousePosition;
        }
        private void paint_MouseMove(object sender, MouseEventArgs e)
        {
            if(mouseClick == true)
           {
               bmp = new Bitmap(300, 300);
               pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
               pictureBox1.Image = bmp;
               gr = Graphics.FromImage(bmp);
               pictureBox1.Refresh();

               breite = e.X - startingpoint.X;
               hoehe = e.Y - startingpoint.Y;
               size.Height = hoehe;
               size.Width = breite;
               Rectangle kreis = new Rectangle(startingpoint, size);
               
               if(rdCircle.Checked == true)
               {
               gr.DrawEllipse(pen, kreis);
               }
               else if(rbRectangle.Checked == true)
               {
               gr.DrawRectangle(pen, kreis); 
               }
            pictureBox1.Refresh();
            }
        }

        private void paint_MouseUp(object sender, MouseEventArgs e)
        {
            mouseClick = false;
            size.Width = 0;
            size.Height = 0;
            breite = 0;
            hoehe = 0;
        }       
       
         private void button1_Click_1(object sender, EventArgs e)
        {
            rdCircle.Checked = false;
            rbRectangle.Checked = false;

            bmp = new Bitmap(300, 300);
            pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
            pictureBox1.Image = bmp;
            gr = Graphics.FromImage(bmp);
            pictureBox1.Refresh();
        }

 private void paint_MouseDown(object sender, MouseEventArgs e)
        {
            mouseClick = true;
            size = new System.Drawing.Size();
            startingpoint = new System.Drawing.Point();
            startingpoint = MousePosition;
        }

private void paint_MouseMove(object sender, MouseEventArgs e)
        {
            if(mouseClick == true)
           {
               bmp = new Bitmap(300, 300);
               pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
               pictureBox1.Image = bmp;
               gr = Graphics.FromImage(bmp);
               pictureBox1.Refresh();

               breite = e.X - startingpoint.X;
               hoehe = e.Y - startingpoint.Y;
               size.Height = hoehe;
               size.Width = breite;
               Rectangle kreis = new Rectangle(startingpoint, size);
               
               if(rdCircle.Checked == true)
               {
               gr.DrawEllipse(pen, kreis);
               }
               else if(rbRectangle.Checked == true)
               {
               gr.DrawRectangle(pen, kreis); 
               }
            pictureBox1.Refresh();
            }
        }

 private void button1_Click_1(object sender, EventArgs e)
        {
            rdCircle.Checked = false;   //Radio Button für Kreis zeichnen
            rbRectangle.Checked = false; // Radio Button für Rechteck zeichnen

            bmp = new Bitmap(300, 300);
            pictureBox1.SizeMode = PictureBoxSizeMode.StretchImage;
            pictureBox1.Image = bmp;
            gr = Graphics.FromImage(bmp);
            pictureBox1.Refresh();
        }

private void paint_MouseDown(object sender, MouseEventArgs e)
{
        this.mouseClick = true;
        this.size.Width = 0;
        this.size.Height = 0;
        this.breite = 0;
        this.hoehe = 0;
        this.startingpoint.X = 0;
        this.startingpoint.Y = 0;
        this.size = new Size();
        this.startingpoint = new Point();
        this.startingpoint = Control.MousePosition;
}

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;

namespace WindowsApplication1
{
    public partial class Form1 : Form
    {
        private Point p;
        private int ellipseHeight;
        private int ellipseWidth;
        private bool mouseDown;

        public Form1()
        {
            InitializeComponent();
        }

        private void pictureBox1_MouseDown(object sender, MouseEventArgs e)
        {
            p.X = e.X;
            p.Y = e.Y;
            mouseDown = true;
            pictureBox1.Refresh();
        }

        private void pictureBox1_MouseMove(object sender, MouseEventArgs e)
        {
            if (mouseDown)
            {
                ellipseWidth = (e.X - p.X); 
                ellipseHeight = (e.Y - p.Y);
                //Ruft Paint() von der PictureBox auf
                pictureBox1.Refresh();
            }
        }

        private void pictureBox1_Paint(object sender, PaintEventArgs e)
        {
            Graphics g = e.Graphics;
            if (mouseDown)
            {
                g.DrawEllipse(Pens.Red, p.X, p.Y, ellipseWidth, ellipseHeight);
            }
        }

        private void pictureBox1_MouseUp(object sender, MouseEventArgs e)
        {
            mouseDown = false;
            p = new Point();
            ellipseWidth = 0;
            ellipseHeight = 0;
        }
    }
}