Of course there are several ways to get photos for any project that you have.
If you frequently need graphics in your work you may already be a member of a stock media service. If not, they are easy to join and great for getting quick access to a large collection of commercially usable photos for your professional or other monetized projects.
If everything you do is completely private and self funded you may be "borrowing" images from the web or elsewhere and using them in your projects.
If you never make any money from those projects you may be within the boundaries of fair use in many cases but beware the use of commercially owned graphics or trademarked images in your monetized products, even if you are "not even making any money with the ads".
If you are a hobbyist or a professional on a shoestring budget and you use media for your monetized or quasi-commercial projects the public domain may be the best choice for you.
