That all depends on the picture. If you have a stock photo that you have purchased or used a free royalty-free image website, it would probably be okay. You would need to check the terms and conditions from the website where you obtained the image. Some, such as Freepik, require you to credit the author of each picture you use.
It would be unacceptable to search Google Images for pictures and then use them without checking whether or not it’s legal to do so.
Here is a list of free image websites.