Create (Add) Transparent Watermark Text to Images (Photo) in ASP.Net using C# and VB.Net

In the same article, you just need to change the Brush

Brush brush = new SolidBrush(Color.Red);

to

Brush brush = new SolidBrush(Color.FromArgb(80, Color.Red));

Opacity values are from 1 - 255.

Less the value the more Transparency you will see.