Far too many businesses still inadvertently steal images online for their website or for their ad campaigns. Copyright law isn't very well known but it is very well enforced. When someone uploads an image to the internet, they own it and unless they specify otherwise, you can not use it unless you get permission (or pay) to use it.
The biggest mistake we've seen businesses make is going to Google Images and doing a search for images, then saving an image and using it. Most of the photos in Google Images are copyrighted. Don't take a chance. Be safe and go to one of these sources:
All three of these have different image sizes you can download and a way to search for an image by category. It may not have exactly what you are looking for but they are high quality images that are free to use.