Can I use royalty-free images for commercial use?
An image that is royalty-free is not necessarily free for commercial use — that is, any use that could lead to buying or selling something. The most reliable image services require you to pay a fee for a license that allows you to use the image for commercial or non-commercial uses, as long as you follow the terms.
How to find free images for commercial use?
Royalty-free images aren't necessarily free. In most cases, you'll have to pay a one-time fee to obtain the rights to use the image. Then you can use it as many times as you like. The free in royalty-free only means that you do not have to pay royalties to the owner of the image every time you use it.