[PHP] drawing problem

I'm able to draw simple figures like squares and circles using ImageCreate(), gd_lib is installed properly as far as I know. But sometimes the result is a little square with a red cross instead of a generated jpg or png. No error messages are shown. Can anyone help me out? Regards, Marco --

[PHP] undefined function imagecreate()

Just new at PHP and learning. Trying to execute simple script to draw a line: ?php //draw2.php Header(Content-type: image/jpeg); $image = ImageCreate(200,150); $gray = ImageColorAllocate($image,204,204,204); $blue = ImageColorAllocate($image,0,0,255); ImageLine($image,10,10,150,30,$blue);