Amin it comes down to the processor your using.
It is quite common to see issues like this with GD2 and there are plenty of examples here. You can raise your PHP memory_limit to say 72MB.
However if your going to use GD2 as your image processor there is no way to upload huge images. GD2 will simply not process huge images since it is part of PHP. If you want to process huge images you need to use Imagemagick and that means your host needs to enable EXEC.