how could create image watermark using ImageMagick

I am trying to convert a 8bp开发者_高级运维p (256) color gif to a 2bpp (4) color gif through ImageMagick.

How can i put an semi-transparent image to the output file in ImageMagick?

You can use ImageMagick's composite command.

Here are a couple links to tutorials and examples of using ImageMagick to add watermarks to your pictures:

• from the ImageMagick help files
• a blog example
• yet another blog example