@aariona - "What is the best and biggest online source for royalty free images to use for blog/graphic design work?"
thadcoxdesign - Never use anything you find on Google as you don't know it's origin and as all of the major stock image sites have bots crawling the internet looking for their images, they will find you and it is always expensive outcome. I know because a client was chased by Getty Images for a tiny picture he used on a 4 year old blog post that he had forgotten about. It cost him around £800 to resolve the situation.
I would always double check before using their images, but I'm pretty sure these sites are good to use:
I also quite like http://photodune.net for paid stock images as although you have to sift through the usual stock image nonsense, there are some lovely shots on there which are $3-$5 but that I have seen for £14-$18 on sites like Creative Market - the exact same pictures!!