So don't think that your projects have to be small. It's better to start big and then resize when you're done. You get much more control that way. You don't start this project by opening a new file, but rather by opening a new idea. With that idea in mind I began to collect images that could act as elements of my project.
Photos are easy to find on the web.
One of the best place that I know of to find images is ArtToday. For a small monthly fee you can download all the photos, clip art and webgraphics you could want. And they are all free for any reasonable use. And the searchable database makes finding your images easy. I went looking for a mountain range for my landscape and a starfield for my sky.