In terms of finding images, I always use google images. Sometimes it means trawling through a lot of photos before I find exactly what I'm looking for, or a little bit of manipulation of images to make them work for me but generally you can find anything you want on there with enough combinations of searches. For example, for one of the up coming World Cup Challenges I wanted a football photo so I searched 'Football' and couldn't find what I wanted and then did 'Soccer Ball' and hey presto! Once I've found sites via google that I find useful I bookmark them for future use. For example, during the election I found the newspaper websites (The Guardian and The Independent especially) had good photo galleries so now I know where to go next time I want to do a news based LO.
There are probably copyright laws and I should be telling you every site I got every photo from when I do that for a LO.