// Image to find inside app window
var sourceImage = System.Drawing.Image.FromFile("C:\\Temp\\NotePad_Edit.png");

// Rectange of the action window
var rect = action.Window.Rectangle;

// Setup graphics objects 
var memoryImage = new System.Drawing.Bitmap(rect.Width, rect.Height);
var memoryGraphics = System.Drawing.Graphics.FromImage(memoryImage);    

// Copy screen pixels of app window
memoryGraphics.CopyFromScreen( 
   rect.X, 
   rect.Y, 
   0, 
   0, 
   new System.Drawing.Size(rect.Width, rect.Height)
);

// Look for sourceImage inside app window pizels/image
var needlePoint = sp.FindImageWithinImage(sourceImage, memoryImage);

// If the sourceImage was found inside the app window's image
if(needlePoint != null) {

    // Translate the coordinates inside the app window to screen coordinates
    var screenPoint = action.Window.ClientPointToScreenPoint(needlePoint);

    // Click Left mouse button in the center of where the sourceImage was found
    sp.MouseClick(
                    new Point(screenPoint.X + parseInt(sourceImage.Width / 2), 
                              screenPoint.Y + parseInt(sourceImage.Height / 2)), 
                    MouseButtons.Left, 
                    true, 
                    true);
}

// Cleanup objects
memoryGraphics.Dispose();
memoryImage.Dispose();
sourceImage.Dispose();