Adding simple test image files

[brendon-boldt]

Would it be possible to add some simple test image files to the repository to make it easier to test edits the codebase. They don't have to be big or anything---just enough to showcase some of the features and cover basic use cases. I have a simple pull request or two that I would like to open, but i would like to test them first. An alternative might be to write a script that creates the images if we want to save on space.