图片水印有两种方法，一是读取水印的所有像素颜色，颜色上加上设置的alpha值，然后将每个像素绘制到指定的位置；二是使用颜色矩阵（
如果忘记了如何使用颜色矩阵的朋友，可以参看《
vb.net 教程 5-16 图像处理之ImageAttributes 类1 颜色矩阵1
》开始的内容），这也是本节所采用的方法。
设计界面，这里测试使用了一个ie的图标作为图片水印：
具体代码：
Private Sub Button2_Click(sender As Object,e As EventArgs) Handles Button2.Click
Dim logoOpacity As Single = HScrollBar1.Value / 255
Dim logoImg As Bitmap = PictureBox2.Image
Dim logoLeft As Integer = 10
Dim logoTop As Integer = 10
Dim imgDest As Bitmap = PictureBox1.Image.Clone
Dim g As Graphics = Graphics.FromImage(imgDest)
Dim matrixArray()() As Single = {
New Single() {1,0},New Single() {0,1,logoOpacity,1}}
Dim cMatrix As New Imaging.ColorMatrix(matrixArray)
Dim imgAttr As New Imaging.ImageAttributes()
imgAttr.SetColorMatrix(cMatrix,Imaging.ColorMatrixFlag.Default,Imaging.ColorAdjustType.Bitmap)
Dim recDest As New Rectangle(logoLeft,logoTop,logoImg.Width,logoImg.Height)
g.DrawImage(logoImg,recDest,logoImg.Height,GraphicsUnit.Pixel,imgAttr)
g.Dispose()
PictureBox3.Image = imgDest
End Sub
下面解释一下代码：
运行结果：