system()/exec() within a PHP script

I need to execute the imagemagick /usr/X11R6/bin/convert program within a php script. The command line: /Absolute-path-to/convert -geometry 150x150 /Absolute-path-to/PHP_image.gif /path-to/PHP_scaledimage.gif works fine from the shell. Within a php script the following line does nothing: system ("/Absolute-path-to/convert -geometry 150x150 /Absolute-path-to/PHP_image.gif /path-to/PHP_scaledimage.gif") I think it's related to some security parameters to not execute some commands from the Web. Directory/files set to 777 and scripts set to 755 SuSE 7.0 PPc Edition PHP 3.03pl1 thanks a lot for you help.