Small image detection in a larger image but with undefined position

If the CAD application can print an area of the overall view, then you can simply print images before and after your changes of that location and compare them. If it can only print the full image, then you can use this method to search for a bitmap image in a larger, or same size, source image. 

It’s complied from several sources, which I can no longer remember…it’s been about 15 years.  I used it as part of an automated testing software that I created, so I know it works well and is very fast. 

It is a static method, and the images need to be bitmaps. There are lots of libraries that can convert PDFs to images, if images are not an option from your CAD package. It will return the location, in pixels, of the smaller image within the larger image as a rectangle.  If the image is not found it will return a rectangle with x, y, width and height with zero values.  The returned rectangle can be used to highlight the location in the source image, if needed.  Of course, it can be modified to just return a Boolean true/false.  I hope this helps.  

This can be complied into a DLL file and used through the DotNet libraires of TestComplete.

  public void Test()
  {
      System.Drawing.Bitmap source = (System.Drawing.Bitmap)System.Drawing.Image.FromFile(@"C:\Source.bmp");

      System.Drawing.Bitmap bmp = (System.Drawing.Bitmap)System.Drawing.Image.FromFile(@"C:\Search2.bmp");

      Rectangle r = source.InImage(bmp);
  }

  public static Rectangle InImage(this System.Drawing.Bitmap src, System.Drawing.Bitmap bmp)
  {
      Rectangle result = default;
      
      if (src== null || bmp == null || bmp.Width > src.Width || bmp.Height > src.Height)
          return result;

      src=(System.Drawing.Bitmap)src.Clone();
      bmp = (System.Drawing.Bitmap)bmp.Clone();

      Rectangle sr = new Rectangle(0, 0, src.Width, src.Height);
      Rectangle br = new Rectangle(0, 0, bmp.Width, bmp.Height);
      BitmapData srcLock = src.LockBits(sr, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
      BitmapData bmpLock = bmp.LockBits(br, ImageLockMode.ReadOnly, PixelFormat.Format24bppRgb);
      int sStride = srcLock.Stride;
      int bStride = bmpLock.Stride;

      checked
      {
          int srcSz = sStride * src.Height;
          int bmpSz = bStride * bmp.Height;
          byte[] srcBuff = new byte[srcSz + 1];
          byte[] bmpBuff = new byte[bmpSz + 1];
          System.Runtime.InteropServices.Marshal.Copy(srcLock.Scan0, srcBuff, 0, srcSz);
          System.Runtime.InteropServices.Marshal.Copy(bmpLock.Scan0, bmpBuff, 0, bmpSz);
          bmp.UnlockBits(bmpLock);
          src.UnlockBits(srcLock);
          int bw = bmp.Width;
          int bh = bmp.Height;
          int sw = src.Width - bw;
          int sh = src.Height - bh;
          int bx;
          int by;
          int num = sh;
          for (int y = 0; y <= num; y++)
          {
              int sy = y * sStride;
              int num2 = sw;
              for (int x = 0; x <= num2; x++)
              {
                  int sx = sy + x * 3;
                  byte r = srcBuff[sx + 2];
                  byte g = srcBuff[sx + 1];
                  byte b = srcBuff[sx];
                  if (r == bmpBuff[2] && g == bmpBuff[1] && b == bmpBuff[0])
                  {
                      result = new Rectangle(x, y, bmp.Width, bmp.Height);
                      int num3 = bh - 1;
                      for (int y2 = 0; y2 <= num3; y2++)
                      {
                          by = y2 * bStride;
                          int num4 = bw - 1;
                          for (int x2 = 0; x2 <= num4; x2++)
                          {
                              bx = by + x2 * 3;
                              sy = (y + y2) * sStride;
                              sx = sy + (x + x2) * 3;
                              r = srcBuff[sx + 2];
                              g = srcBuff[sx + 1];
                              b = srcBuff[sx];
                              if (r != bmpBuff[bx + 2] || g != bmpBuff[bx + 1] || b != bmpBuff[bx])
                              {
                                  result = default;
                                  sy = y * sStride;
                                  break;
                              }
                          }
                          if (result == default)
                              break;
                      }
                  }
                  if (result != default)
                      break;
              }
              if (result != default)
                  break;
          }
          return result;
      }
  }