Citing Photos for Keynote

I understand how to do the citation of photos, but what is the real point of Citing these images, especially because most were picked up on Google images, so technically they understood that before they allowed google to pick up links to their site that they were offering their images for free. It just seems a little redundant to cite what was practically "given up" by the people who made them, but that's just my opinion and most likely i got the whole system wrong so if anyone has more info on this subject don't hesitate to post a comment ^^.

PS: Again, this is in my opinion and I'm open to other opinions with or against my claim.