Ayuda en c# con poner imagen sobre imagen

En un principio yo también veo mal ofrecer ayuda a quien lo pide todo hecho sin mostrar código alguno, pero me he dado cuenta de que un "ejercicio" o utilidad cómo esta me faltaba en mi librería personal de códigos y me ha llamado la atención el desarrollar este tipo de utilidad para un uso genérico, ya que lo hago pues lo comparto.

Imagen trasera e imagen delantera

Superposición (opaca)

Código fuente

Código

    ''' <remarks>
    ''' *****************************************************************
    ''' Snippet Title: Overlay Images
    ''' Code's author: Elektro
    ''' Date Modified: 30-April-2015
    ''' *****************************************************************
    ''' </remarks>
    ''' <summary>
    ''' Overlay an image over a background image.
    ''' </summary>
    ''' <param name="backImage">The background image.</param>
    ''' <param name="topImage">The topmost image.</param>
    ''' <param name="topPosX">An optional adjustment of the top image's "X" position.</param>
    ''' <param name="topPosY">An optional adjustment of the top image's "Y" position.</param>
    ''' <returns>The overlayed image.</returns>
    ''' <exception cref="ArgumentNullException">backImage or topImage</exception>
    ''' <exception cref="ArgumentException">Image bounds are greater than background image.;topImage</exception>
    Public Shared Function OverlayImages(ByVal backImage As Image,
                                         ByVal topImage As Image,
                                         Optional ByVal topPosX As Integer = 0,
                                         Optional ByVal topPosY As Integer = 0) As Image
 
        If backImage Is Nothing Then
            Throw New ArgumentNullException(paramName:="backImage")
 
        ElseIf topImage Is Nothing Then
            Throw New ArgumentNullException(paramName:="topImage")
 
        ElseIf (topImage.Width > backImage.Width) OrElse
               (topImage.Height > backImage.Height) Then
            Throw New ArgumentException(message:="Image bounds are greater than background image.", paramName:="topImage")
 
        Else
            topPosX += CInt((backImage.Width / 2) - (topImage.Width / 2))
            topPosY += CInt((backImage.Height / 2) - (topImage.Height / 2))
 
            Dim bmp As New Bitmap(backImage.Width, backImage.Height)
 
            Using canvas As Graphics = Graphics.FromImage(bmp)
 
                canvas.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic
 
                canvas.DrawImage(image:=backImage,
                                 destRect:=New Rectangle(0, 0, bmp.Width, bmp.Height),
                                 srcRect:=New Rectangle(0, 0, bmp.Width, bmp.Height),
                                 srcUnit:=GraphicsUnit.Pixel)
 
                canvas.DrawImage(image:=topImage,
                                 destRect:=New Rectangle(topPosX, topPosY, topImage.Width, topImage.Height),
                                 srcRect:=New Rectangle(0, 0, topImage.Width, topImage.Height),
                                 srcUnit:=GraphicsUnit.Pixel)
 
                canvas.Save()
 
            End Using
 
            Return bmp
 
        End If
 
    End Function

Traducción online a C#

Código

/// <remarks>
/// *****************************************************************
/// Snippet Title: Overlay Images
/// Code's author: Elektro
/// Date Modified: 30-April-2015
/// *****************************************************************
/// </remarks>
/// <summary>
/// Overlay an image over a background image.
/// </summary>
/// <param name="backImage">The background image.</param>
/// <param name="topImage">The topmost image.</param>
/// <param name="topPosX">An optional adjustment of the top image's "X" position.</param>
/// <param name="topPosY">An optional adjustment of the top image's "Y" position.</param>
/// <returns>The overlayed image.</returns>
/// <exception cref="ArgumentNullException">backImage or topImage</exception>
/// <exception cref="ArgumentException">Image bounds are greater than background image.;topImage</exception>
public static Image OverlayImages(Image backImage, Image topImage, int topPosX = 0, int topPosY = 0)
{
 
        if (backImage == null) {
		throw new ArgumentNullException(paramName: "backImage");
 
	} else if (topImage == null) {
		throw new ArgumentNullException(paramName: "topImage");
 
	} else if ((topImage.Width > backImage.Width) || (topImage.Height > backImage.Height)) {
		throw new ArgumentException("Image bounds are greater than background image.", "topImage");
 
	} else {
		topPosX += Convert.ToInt32((backImage.Width / 2) - (topImage.Width / 2));
		topPosY += Convert.ToInt32((backImage.Height / 2) - (topImage.Height / 2));
 
		Bitmap bmp = new Bitmap(backImage.Width, backImage.Height);
 
		using (Graphics canvas = Graphics.FromImage(bmp)) {
			canvas.InterpolationMode = Drawing2D.InterpolationMode.HighQualityBicubic;
			canvas.DrawImage(image: backImage, destRect: new Rectangle(0, 0, bmp.Width, bmp.Height), srcRect: new Rectangle(0, 0, bmp.Width, bmp.Height), srcUnit: GraphicsUnit.Pixel);
			canvas.DrawImage(image: topImage, destRect: new Rectangle(topPosX, topPosY, topImage.Width, topImage.Height), srcRect: new Rectangle(0, 0, topImage.Width, topImage.Height), srcUnit: GraphicsUnit.Pixel);
 
			canvas.Save();
		}
		return bmp;
	}
}
 
//=======================================================
//Service provided by Telerik (www.telerik.com)
//=======================================================

Modo de empleo (el mismo que he usado para generar el ejemplo de superposición de arriba)

Código

Dim backImg As Image = Image.FromFile("C:\back.jpg")
Dim topImg As Image = Image.FromFile("C:\top.png")
Dim overlay As Image = OverlayImages(backImg, topImg, topPosX:=+5, topPosY:=-15)
overlay.Save("C:\Overlay.jpg", Imaging.ImageFormat.Jpeg)
Process.Start("C:\Overlay.jpg")

Saludos