For example, in examining an image of a section of a river, you should understand the full flow of the river. The big picture and small details inform each other. Often the most fruitful lines of investigation derive from mysteries. The more students study images, the more observant they will be of anomalies, and the more these anomalies will spark their curiosity. Stay with the image for a while.
Scientists often spend an extended period of time examining individual images.
The longer they look, the more they see. So encourage your students to stick with their investigation, going deeper and extending it in new directions. To investigate an image, your students should cross-reference with other resources. Encourage your students to look at physical and political maps of the same region, compare with thematic maps showing vegetation or population patterns and learn about the human and geologic history of the region. The more your students learn and the richer the variety of resources, the more they will see in the images.