Thyrosis did answer your last question. Sounds like you're slightly confused with the differences between a graphics library and graphics software.?
The image created with GD is a static image, and cannot be edited
The GD Library is a set of functions for creating images on the fly much like your graphics software. The key difference is that with this library you have to create the tools to make it work where graphics software has done all the hard work for you. Both end up with a final static image.
As with these two function calls:
// This will created some text with a dark shadow up-right from the original text
imagettftext ( resource $image , float $size , float $angle , int $x , int $y , int $lightcolor , string $fontfile , string $text )
imagettftext ( resource $image , float $size , float $angle , int $x+4 , int $y-4 , int $darkcolor , string $fontfile , string $text )
In graphics software each would be an object contained in another object say a 'Text' object. So you would use a form to change the text and an option to show a shadow or not. But the new object still has to be re-drawn for display.
Anyway hope that helps...