How to use ImageMagick to substract a image from another?

I have this two images :

_{(source: free.fr)}

_{(source: free.fr)}

How can I use imagemagick to remove the background (second picture) from the first one ?

Cheers,

Rémy

Here I made you a final but simple example :

Transparent Overlay http://noosphere.开发者_高级运维ionyse.com/transparent_example/transparent_difference.png Background http://noosphere.ionyse.com/transparent_example/background.png

Example 1 http://noosphere.ionyse.com/transparent_example/background-example.png Example 2 http://noosphere.ionyse.com/transparent_example/background-example2.png

Here you see that anywhere I put the transparent overlay on the background I get the perfect match using the opacity of the overlay PNG.

I would like to be able to calculate this overlay image. Do you think it is possible using ImageMagick ?

This is explained over here How to save the DIFFERENCES between two images ?.

Another useful link: http://www.imagemagick.org/Usage/compare/#difference