Do I have to copy all pixels over to make a sub image?

Processing or even SFML made it easy to grab a sub image out of an old image without having to copy over each pixel, I cant seem to find any documentation on easy sub images, why is this?

Sorry – is your question why you can’t find documentation or how to create sub-images without copying pixels?

I found crop since, im just getting really frustrated with the lack of documentation, I am generally struggling to find examples and tutorials but since have found the crop function, Ido know how to copy images without having to go through pixel manipulation now, but somehow i got the impression it was the only way!