If the crankie will be performed to a live audience, I try to keep in mind, that person in the last row. A seventeen inch high screen is not that big, so I try to make the images large and salient
so that the people will be able to recognize what the image is. It doesn't mean that you can't have detail, but the images should be recognizable from a good distance.
I use Google images
A LOT. Not only for examples of images, but to get ideas for scenes.
Here are some examples of planning sketches from various artists.