private System.Drawing.Image Watermark(ref System.Drawing.Image sourceImage, ref System.Drawing.Image watermarkImage, int x, int y, int opacity = 30)
{
    Bitmap srcImage = new Bitmap(sourceImage);
    Bitmap wtrImage = new Bitmap(watermarkImage);

    if (opacity < 0) { opacity = 0; }
    if (opacity > 100) { opacity = 100; }

    float opaque = (opacity / 100.0f);

    using (Graphics g = Graphics.FromImage(srcImage))
    {
        System.Drawing.Imaging.ColorMatrix matrix = new System.Drawing.Imaging.ColorMatrix(
            new float[][]
            {
                new float[] {1, 0, 0, 0, 0},
                new float[] {0, 1, 0, 0, 0},
                new float[] {0, 0, 1, 0, 0},
                new float[] {0, 0, 0, opaque, 0},
                new float[] {0, 0, 0, 0, 1}
            });

        System.Drawing.Imaging.ImageAttributes attributes = new System.Drawing.Imaging.ImageAttributes();
        attributes.SetColorMatrix(matrix);

        g.DrawImage(wtrImage, new Rectangle(x, y, wtrImage.Width, wtrImage.Height), 0, 0, wtrImage.Width, wtrImage.Height, GraphicsUnit.Pixel, attributes);
    }

    return srcImage;
}

Posted: March 19, 2023

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