http://www.getafreelancer.com/projects/PHP/PHP-Image-transparancy-convert.268512.html
This project consist of 3 parts:
First part was implemented in the latest GD, so it's no code.
Second part – YetiLib.php – is ready for use. Here is a Demo.
Third part was made using the Alladin(C) GhostScript engine.
Here you can see the working demo of the library:
Image logo transparancy | EPS2JPG/PDF2JPG