A client of mine wants to use photos off the internet for her book that will be printed on a small run from 50-200 for clients of hers for a training manual.
How do i cite them properly to cover both of us for copyright?
You can not just use pictures from online sources without first looking up the license of each and every picture. No amount of citing the source will make it permissible to use images. Only the licensing condition applies, this is not a fair use condition by any stretch. Manuals don't fall under any of the common exceptions, although legal issues vary based on where you are located.*
So once you have figured out what the license of the image is you have to read how the license specifies you do this, then repeat for all images separately. Yes that means that some images have to be handled differently from other images. Be sure to bill you client for doing this work. Even if the image is free of monetary charge does not mean that the licensing can not put a cost on you or your client.
* I am not a lawyer - Worse, I am not your lawyer
You should be able to get a long way with CC-BY-licensed pictures. Google image search has this as an option but it's not perfect so you need to check.
Finding the CC images takes time. Checking the licenses takes time. The client has to pay somehow, whether that's on your bill or by getting the images themselves.
You might want to take a look at Pexels as well, as it provides wonderful CC-licensed images.