In a typical assignment, you don't have to worry about the licensing terms of a photograph - as long as you cite your source you are able to use almost any image you find online or in a print source. If you're going to "publish" something things are a little different - and we're going to think of our StoryMaps as a published item. When we're publishing something (that is, sharing is broadly online or in print) we need to make sure that we have the right to re-share the images we include. The easiest way to do this is to search in sources we trust to provide us with the complete and correct licensing information for images.
Important note: While some Creative Commons (CC) licenses do not specify that you need to make attribution (give credit) to the creator - even if this is the case you must properly cite the image for your assignment