¿no se te ha ocurrido revisar en el
manual de php?:
# imagecopy — Copy part of an image
# imagecopymerge — Copy and merge part of an image
# imagecopymergegray — Copy and merge part of an image with gray scale
# imagecopyresampled — Copy and resize part of an image with resampling
# imagecopyresized — Copy and resize part of an image