How do you make a visual impact?
There are, of course, rules of aesthetics--composition, complementary colors, and typography for example. Yet one of the simplest and often overlooked concepts is keeping your imagery general and abstract rather than specific and concrete.
In other words, a simple sketch will suggest and evoke emotion more than, say, a photograph. It's rather like reading a book, wherein the images play out in your imagination, over against watching the movie version.
For example, a sketch of a waterfall evokes the idea of falling water better than a photograph of a single, specific waterfall. The viewer may then be thinking, 'is that Niagara Falls? Or Yellowstone?"
Or, an illustration of a deer might evoke better the idea of "As the deer pants for water, so my soul longs for you, O Lord" than a photo of a white-tailed deer ("is it hunting season yet?") or a prong-horn antelope ("Did the Psalmist have antelope in Israel?")
Generally, photos are less impactful on the imagination because they are specific and concrete. They record a specific thing in a specific setting. A more abstract, blurred, or partial image is often a better choice for conveying emotion without introducing distracting details.
And the good news is you can probably do some basic sketches yourself! That avoids all copyright issues and gives you the freedom to express your point more clearly.
So feel free to do some drawing! It may pack more of a whollup!
[This article explores the value of abstraction in terms of web design.]