I call the function createImageFromJpeg like the documentation tells:

*************

function myFunction($cImagefile) {
   $oImage = ImageCreateFromJpeg($cImagefile);

   if(!$oImage) // Error
      return false;
   else
      return true;
}

*************

I think $oImage will be invalid if $cImagefile is a uncomplete jpeg-file (the upload of the picture didn't finished) and my function will return false.
But Apache 2 takes 99% of CPU and hangs.

I have to stop the Apache 2 service and restart.

The "error/problem" doesn't appear with a completely uploaded jpeg-file because ImageCreateFromJpeg returns a valid image-ressource