Whoever creates content (e.g. poems - stories - articles - photos - artwork) owns the copyright to that content. If others want to use it they will need to cite the content by giving the owner credit.
When a for-profit business wants to use an image or a narrative, they pay the creator or create one in-house.
There are organization and collectives that supply open access images that you can use in papers, power points and poster presentations.
You can also see some of these in a Google search. Here is how it works. Search for an image - click on image and then click on tools. In this example we have selected "labeled for reuse".