There are lots of ways to include visualizations on your poster - graphs, charts, photographs, as well as many others.
I used Wordle to create this tag cloud, then I took a screen shot of the image to put on this guide for you. There are other tag cloud generators out there and lots of best practices.
One way to add meaning to your poster is to use images.
Generally speaking, photos as background images rarely look good. The image tends to overpower the text and make the poster hard to read. (If you must, you can fade out your image by using image editing software.) Instead, try using a background color or boxes to set off your text and images.