As Jack said absolutely do
NOT use Google images.
99.9% of the images you'll see on there will be illegal to use, and the companies that own them (Getty Images being the largest in the world) use very sophisticated software to track websites (and Facebook) for illegal use of images/photos. Like Jack, I've had people illegally use my designs too, and I don't hesitate about sending C+D letters out. It's my livelihood and my clients brands that I need to protect.
Just Google "the getty letter" and you'll never be tempted to do that.
The real cost of being sued by Getty | Copyright Action
To be honest, for something so seemingly simple, its a mine-field. Simply because the stock photo industry is worth millions of dollars.
The rule you should stick to (to never be in a position where you'll be sued for hundreds/thousands of pounds) is that you can
only use images that have been designed for you, or that you've purchased directly.
In either case, ask the designer if he or she has sourced legal images (you'll be surprised how many of them use illegal images, including large high-street chains- but that's another story), and you MUST keep any receipts for the photos you've bought.
To answer your question more specifically, it depends what you mean by "images", do you mean graphics or photos? And do you mean for print? or for the web?
The first thing I do when people ask me the best place for photos is refer them to their suppliers. Many suppliers will be happy to share images with you. It's a win-win for them in that the more professional you look, the more product you'll flog.
Many of the "Happy New Year" images for Facebook you've seen are created by designers like me. I spend a lot of time on Facebook these days and I've seen lots and lots of badly pixelated, rough covers that are just taken from "free" sites and are pretty unprofessional. Most of my clients have people like me design them with their logo/branding on to make them more personal.
If your suppliers can't help you, and you're looking for photos then the places mentioned above are where you should go. However, two things to bear in mind with using them too.
1. Make sure the resolution is correct. If you're buying for the web you need 72dpi images, if you're buying for print buy 300dpi images. If you're budget allows, always get the 300dpi version, as you'll be able to use it for both print and web!
2. Check the terms and conditions of the photo. Many, many people don't do this. Most people assume once you've bought an image you can use it for whatever you like, as many times as you like, and that is not the case at all. Many stock photo places have different terms and conditions and you must check these before purchase to make sure you're ok. For example Shutterstock will let you purchase images on a "standard" license, but you'll find that you can't use many of those images for business use and you should have bought the (much more expensive) "enhanced" licensed.
All
very dull I know.
But, it's important as sueing people for use of illegal images is a fantastic source of revenue for these multi-national corporations, and you'd be silly not to take it seriously.
p.s. Don't think that it'd make a difference to them if you're a huge company or a one-man band...they'll find you and sue!