Installed version

Find the installed version of ImageMagick being used by php

echo "<pre>";
system("convert -version");  


Version: ImageMagick 6.3.4 05/11/07 Q16
Copyright: Copyright (C) 1999-2007 ImageMagick Studio LLC

Note: You could have multiple versions installed and this will confirm which version php is using. It could a different version than using Imagemagick directly from the command line.
You might not get a version number returned and then you would need to add the path to convert - see Path