Ben CentOS 5.5, PHP 5.1.6, Apache/2.2.3 ImageMagick 6.2.8 çalışan bu kodu var

$convert = "/usr/bin/convert";
$command = "$convert -size 100x100 xc:blue mytest.jpg";
$test_image = exec($command);
echo "<img src=\"mytest.jpg\">";

when i run the php tester i dont get the image created , only the echo string printed on page as html.
but when i run the same command as onliner the image does created just fine.

/usr/bin/convert -size 100x100 xc:blue mytest.jpg

neyin yanlış olduğunu burada ben söyleyemem.