I use image google a LOT for making school materials or for searches. However, it can take quite a while to find a copyright-free image for a printable to share or, if I ever get my cottage industry going, to sell. I have 2 favorite clip art sources, one free and one subscription.
The free one is WPClipart and it has the added bonus that you can put a button on your computer to access it easily. They have already searched the copyrights of images for you and any of these are free to use. I have used this for years with no problems.
The subscription clip art service is Graphics Factory. I had it for a year and used it a lot. I let it expire last year but just renewed again. Just in time too because I'm working on the economic geography "stamps" and am making a Wild West lapbook from scratch. These will both need a lot of graphics. I really enjoyed having the subscription that year and used it a lot.
Why am I telling you this? Because I just saw last night that they have their year-long subscription (maybe all of their subscriptions) on sale for 50% off! I'm not sure how long this will last. A few weeks ago I checked and although it was on sale it wasn't this good - so glad I waited! Here is the main link:
No, I do not get anything from this positive review. It's purely altruistic :)