I always keep a supply of interesting photos (and illustrations), cut from magazines and newspapers, in a basket for writing prompts. They are great to use when students are stuck and can't think of anything to write about.

A lesson can also be done with them: Start by having a couple of students pick a picture at random and bring it to the front of the room. Have them talk about what they see and imagine what kind of story they could write about it. Then have other students ask questions about the picture, to encourage more details. Pass out pictures to all students and tell them they are going to imagine a story about the picture. They can brainstorm first (graphic organizers work well here if you have a supply on hand, or check online for some), and write all the things they think about when they look at the picture. Remind about needing a beginning, middle, and ending to the story. Have students write a draft then follow through the writing process to a good copy. Share stories while showing pictures.

This lesson encourages students to expand on ideas, and look closely at details in pictures.