There are all kinds of ways to insert photos into a post or page. You don’t need to use the WP gallery functions or third-party sliders, you can just insert the photos directly onto the page. You can choose original size, full size, medium size or thumbnails. It’s not always the best solution, but it gives you a bit of control as to where and how your photos are laid out on the page. For example, this is a good way to put in a single photo when you have text. But for galleries, there are better options.